Chemical engineering Doctoral dissertation: Synthesis of catalysts based on Pt/SBA-15 modified with Al and/or B and their applicability on n-heptane hydroisomerization, tetralin hydrogenation and paracetamol detection

MINISTRY OF EDUCATION AND TRANING

HANOI UNIVERSITY OF SCIENCE AND TECHNOLOGY

NGO THI THANH HIEN

Synthesis of catalysts based on Pt/SBA-15 modified with Al and/or B and

their applicability on n-heptane hydroisomerization, tetralin

hydrogenation and paracetamol detection

CHEMICAL ENGINEERING DOCTORAL DISSERTATION

Ha Noi – 2020

MINISTRY OF EDUCATION AND TRANING

HANOI UNIVERSITY OF SCIENCE AND TECHNOLOGY

NGO THI THANH HIEN

Synthesis of catalysts based on Pt/SBA-15 modified with Al and/or B and

their applicability on n-heptane hydroisomerization, tetralin hydrogenation

and paracetamol detection

Major: Chemical Engineering

Code No: 9520301

CHEMICAL ENGINEERING DOCTORAL DISSERTATION

ADVISORS:

1. Assoc. Prof. Pham Thanh Huyen

2. Prof. Graziella Liana Turdean

Ha Noi – 2020

STATUTORY DECLARATION

I hereby declare that I myself have written this thesis book. The data and

results presented in the dissertation are true and have not been published by other

authors.

Ha Noi, 25th September 2020

PhD Student

Ngo Thi Thanh Hien

ADVISORS:

1. Assoc.Prof. Pham Thanh Huyen

2. Prof. Graziella Liana Turdean

ACKNOWLEDGEMENT

First of all, I would like to thank my advisors Assoc. Prof. Dr Pham Thanh Huyen

and Prof. Dr. Graziella Liana Turdean for all support and encouragement which

really helped me and motivated me during my research.

I would like to thank Prof. Vasile I. Parvulescu at Deparment of Organic Chemistry,

Biochemistry and Catalysis, University of Bucharest, Romania for the support in

hydroisomerization experiments.

I would like to thank my friends at HaNoi University of Science and Technology

(HUST) and at “Babes- Bolyai” University (UBB) for all assistances and for the

enjoyable time, friendly events we shared together.

I would like to acknowledge the Eramus+ Program with partner countries for the

financial support of my stages at “Babes- Bolyai” University, Cluj –Napoca,

Romania.

I want to extend my thanks to Assoc. Prof Do Ngoc My – Rector of QuyNhon

University (QNU), Dr. Nguyen Le Tuan – Former Dean of Faculty of Chemistry,

Dean of Faculty of Natural Sciences - QNU and my colleagues at QNU for their

support.

Finally, I would like to express my deep thanks to my family for all their love,

encouragement and unconditional support throughout my PhD studying.

CONTENTS

STATUTORY DECLARATION ------------------------------------------------------------ i

ACKNOWLEDGEMENT ------------------------------------------------------------------- ii

CONTENTS ----------------------------------------------------------------------------------- iii

LIST OF ABBREVIATIONS ------------------------------------------------------------- vii

LIST OF FIGURES -------------------------------------------------------------------------- ix

LIST OF TABLES -------------------------------------------------------------------------- xiii

INTRODUCTION ----------------------------------------------------------------------------- 1

THE NEW CONTRIBUTION OF THE DESSERTATION-------------------------- 4

CHAPTER 1. LITERATURE REVIEW ------------------------------------------------- 5

1.1. Mesoporous material and ordered mesoporous silica SBA-15 ------------------- 5

1.2. The modified SBA-15 materials and applications --------------------------------- 6

1.3. The hydroisomerization of n-alkane over bifunctional catalysts ---------------- 10

1.3.1. Metal function of bifunctional catalysts -------------------------------------- 11

1.3.2. Acid function of bifunctional catalysts --------------------------------------- 12

1.4. Hydrogenation of polynuclear aromatic hydrocarbon (PAHs) ------------------ 17

1.4.1. Hydrogenation of polynuclear aromatic hydrocarbon (PAHs) ------------ 17

1.4.2. Catalysts for PAHs hydrogenation -------------------------------------------- 20

1.5. Overview of paracetamol detection. ------------------------------------------------ 24

1.5.1. Introduction of paracetamol ---------------------------------------------------- 24

1.5.2. Electroanalytical methods based on using chemically modified electrodes (CMEs) for paracetamol detection. -------------------------------------- 25

1.5.3. Chemically modified electrodes (CMEs) for PA detection ---------------- 30

1.6. Conclusions ---------------------------------------------------------------------------- 35

CHAPTER 2. EXPERIMENTAL --------------------------------------------------------- 37

2.1. Preparation of catalysts --------------------------------------------------------------- 37

iii

2.1.1. Direct synthesis procedure of M-SBA-15 (where M=Al and/or B) ------- 37

2.1.2. Indirect synthesis of B/SBA-15 ------------------------------------------------ 38

2.1.3. Synthesis of Pt/M-SBA-15 (where M=Al-, B- and Al-B-) catalysts ------ 38

2.2. Electrochemical procedure ----------------------------------------------------------- 38

2.2.1. Preparation of Pt/M-SBA-15-GPE electrodes ------------------------------- 38

2.2.2. Preparation of supporting electrolyte and standard solution of paracetamol ------------------------------------------------------------------------------- 39

2.3. Catalyst characterization techniques ------------------------------------------------ 40

2.3.1. X-Ray Diffraction --------------------------------------------------------------- 40

2.3.2. Transmision electron microscopy (TEM) ------------------------------------ 41

2.3.3. Fourier Transformed Infrared Spectroscopy (FT-IR) ----------------------- 41

2.3.4. Temperature Programmed Desorption (NH3-TPD) ------------------------- 42

2.3.5. Nitrogen adsorption-desorption ------------------------------------------------ 42

2.3.6. Thermal analysis ----------------------------------------------------------------- 43

2.3.7 Inductively coupled plasma optical emission spectrometry (ICP - OES) 44

2.3.8. Pyridine-FTIR -------------------------------------------------------------------- 44

2.3.9. Energy Dispersive X-Ray Spectroscopy (EDS or EDX) ------------------- 44

2.3.10. 11B MAS NMR spectrocopy ------------------------------------------------- 45

2.4. Hydroisomerization activity test----------------------------------------------------- 45

2.5. Hydrogenation activity test ----------------------------------------------------------- 45

2.6. Electrochemical measurements ------------------------------------------------------ 46

CHAPTER 3. RESULTS AND DISCUSSION ----------------------------------------- 49

3.1. Effect of preparation methods of support.------------------------------------------ 49

3.2. Characterizations of modified SBA-15 supports ---------------------------------- 53

3.2.1. X-ray diffraction (XRD) -------------------------------------------------------- 54

3.2.2. Nitrogen physisorption isotherms. --------------------------------------------- 54

3.2.3. Transition electron microscopy (TEM) --------------------------------------- 56

3.2.4. Fourier-transform infrared spectroscopy (FTIR) --------------------------- 57

3.2.5. EDX analysis --------------------------------------------------------------------- 58

3.2.6. 11B MAS-NMR spectroscopy ------------------------------------------------- 60

3.2.7. Ammonia Temperature- Programmed Desorption (NH3-TPD) ----------- 60

3.2.8. FTIR spectra of chemisorbed pyridine ---------------------------------------- 63

3.3. Characterizations of Pt/modified SBA-15 catalysts ------------------------------ 63

3.3.1. Nitrogen physisorption isotherms---------------------------------------------- 63

3.3.2. X-ray diffraction (XRD) -------------------------------------------------------- 64

3.3.3. Transition electron microscopy (TEM) --------------------------------------- 65

3.3.4. NH3-TPD profiles --------------------------------------------------------------- 65

3.4. Performance of platinum supported on modified SBA-15 catalysts for hydro- isomerization of n-heptane ---------------------------------------------------------------- 68

3.4.1. Effect of the acidic supports on hydroisomerization activity of catalysts 68

3.4.2. Effect of temperature and reaction time in the hydroisomerization of n- heptane ------------------------------------------------------------------------------------ 70

3.4.3. Cracked product yield and coke formation ----------------------------------- 72

3.5. Performance of platinum supported on modified SBA-15 catalysts for hydrogenation of tetralin ------------------------------------------------------------------- 75

3.5.1. The results of GC-MS analysis of hydrogenation of tetralin --------------- 75

3.5.2. Effect of reaction temperature and pressure on catalytic activity --------- 76

3.5.3. Effect of the acidity of modified supports on catalytic activity. ----------- 78

3.5.4. Coke formation ------------------------------------------------------------------- 80

3.6. The mesoporous catalysts of Pt loaded on modified SBA-15 material for the paracetamol detection ---------------------------------------------------------------------- 82

3.6.1. Characterization of 1%Pt/Al-SBA-15 catalyst ------------------------------ 83

3.6.2. Electrochemical characterization of Pt/Al-SBA-15-GPE electrode material ----------------------------------------------------------------------------------- 85

3.6.3. Electrochemical impedance spectroscopy measurements at Pt/Al-SBA- 15-GPE electrode ------------------------------------------------------------------------ 88

3.6.4. Analytical characterization of Pt/Al-SBA-15-GPE electrode material --- 89

3.6.5. Interference study ---------------------------------------------------------------- 91

3.6.6. Real sample analysis------------------------------------------------------------- 92

CONCLUSIONS ------------------------------------------------------------------------------ 94

PUBLICATIONS OF THE DISSERTATION ----------------------------------------- 96

REFERENCES -------------------------------------------------------------------------------- 97

LIST OF ABBREVIATIONS

Ascorbic acid AA

Brunauer-Emmet-Teller BET

Counter electrode CE

CMEs Chemically modified electrodes

Cetane Number CN

Cyclic voltammetry CV

Differential thermal analysis DTA

Electrochemical impedance spectroscopy EIS

Fluid catalytic cracking FCC

Fourier transformed infrared spectroscopy FT-IR

Full width at half maximum FWHM

Glassy carbon electrode GCE

Graphite paste electrode GPE

Inductively coupled plasma method ICP

Light cycle oil LCO

Limit of detection LOD

Amorphous silica-alumina MSA

NH3-TPD Ammonia Temperature- Programmed Desorption

Paracetamol PA

Polynuclear aromatic hydrocarbons PAHs

Phosphate buffer solution PBS

Py-FTIR FTIR spectra of chemisorbed pyridine

RE Reference electrode

vii

SAPO-n Silicoaluminophosphate

SBA-15 Santa Barbara Amorphous No 15

Square wave voltammetry SWV

Transmision electron microscopy TEM

Tetraethyl orthosilicate TEOS

Thermogra vimetric analysis TGA

TMOS Tetramethyl orthosilicate

Uric acid UA

Working electrode WE

viii

X-ray diffraction XRD

LIST OF FIGURES

Fig 1.1. Formation mechanism of MCM-41 suggested by Beck et al ......................5

Fig 1.2. Co-condensation approach for the functionalization of mesoporous materials .................................................................................................................7

Fig 1.3. Functionalization of SBA-15 through post-grafting ....................................7

Fig 1.4. Formation of Bronsted acidic site in mesoporous materials ........................8

Fig 1.5. Two different tetrahedral structures of boron in B-SBA-15 framework ......8

Fig 1.6. Scheme of n-alkane hydroisomerization over bifunctional catalysts ......... 10

Fig 1.7. Stepwise hydrogenation of an adsorbed tetralin molecule to cis- and trans- decalin .................................................................................................................. 17

Fig 1.8. Reaction network of tetralin hydrocracking .............................................. 18

Fig 1.9. Cetane number (CN) of some possible products of naphthalene hydrogenation (CN values according to Santana et al). .......................................... 19

Fig 1.10. Reaction scheme for the selective hydrocracking of tetralin into BTX ... 19

Fig 1.11. Chemical structure of PA ........................................................................ 24

Fig 1.12. Electrochemical oxidation of PA ............................................................ 24

Fig 1.13. Cyclic potential sweep (a) and resulting cyclic voltammogram (b) ......... 27

Fig 1.14. Cyclic voltammogram of a reversible reaction system (a), quasi-reversible system (b) and irreversible reaction system (c) ...................................................... 27

Fig 1.15. (a) Scheme of application of potentials of square wave voltammetry method. (b) The response contains a forward (anodic, I(1)), backward (cathodic, I(2)) and net current ΔI ......................................................................................... 28

Fig 1.16. The relation of a real part (Z’) and an imaginary part (Z”) in the complex plane. ..................................................................................................................... 29

Fig 1.17. The Randles equivalent circuit- frequently used to represent an electrochemical cell. [95]. Where: Cdl: capacitance of the double layer charging; Rsol: the solution resistance; Zf: the impedance of the faradic process. ................... 30

Fig 2.1. Direct-synthesis of M-SBA-15 (M = Al and/or B) .................................... 37

Fig 2.2. Synthetic procedure of Pt supported on modified supports (Al-SBA-15; Al- B-SBA-15; B-SBA-15) ......................................................................................... 39

Fig 2.3. Schematic illustration of diffraction according to Bragg’s law. ................. 40

Fig 2.4. (a) The high pressure autoclave batch reactor and (b) schematic batch reaction system used for the n-heptane hydroisomerization and the tetralin hydrogenation ........................................................................................................ 46

Fig 2.5. Cyclic voltammogram for a reversible system .......................................... 47

Fig 3.1. Low angle XRD patterns of SBA-15, B/SBA-15 and B-SBA-15 .............. 49

Fig 3.2. TEM images of SBA-15 (A), B-SBA-15 (B) and B/SBA-15(C) ............... 50

Fig 3.3. Nitrogen adsorption–desorption isotherm (A) and BJH pore size distribution (B) of SBA-15, B-SBA-15 and B/SBA-15 ......................................... 51

Fig 3.4. NH3-TPD curves of SBA-15; B-SBA-15 and B/SBA-15........................... 52

Fig 3.5. Low angle XRD patterns of SBA-15; M-SBA-15 (M=Al and/or B) samples. ................................................................................................................. 54

Fig 3.6. Nitrogen adsorption isotherms and (A) Pore size distribution of SBA-15; Al-SBA-15, Al-B-SBA-15; B-SBA-15 (B). ........................................................... 55

Fig 3.7. TEM images of SBA-15 (A); Al-SBA-15 (B); Al-B-SBA-15 (C) and B- SBA-15 (D) ........................................................................................................... 57

Fig 3.8. FTIR spectra of SBA-15 and modified SBA-15 samples ........................... 58

Fig. 3.9. EDX spectras of Al-SBA-15 (A); Al-B-SBA-15 (B); B-SBA-15 (C) ....... 59

Fig 3.10. 11B MAS-NMR for B-SBA-15 sample ................................................... 60

Fig 3.11. NH3-TPD curves of Al-SBA-15; Al-B-SBA-15; B-SBA-15 samples ..... 61

Fig. 3.12. The Py-FTIR spectras of Al-SBA-15 (A), Al-B-SBA-15 (B), B-SBA-15 (C) ......................................................................................................................... 62

Fig. 3.13. Nitrogen adsorption-desorption isotherms and pore size distribution of catalysts. ................................................................................................................ 64

Fig 3.14. Low angle XRD patterns 0.5%Pt/Al-SBA-15 (A); 0.5%Pt/Al-B-SBA-15 (B) and 0.5%Pt/B-SBA-15 (C) catalysts ................................................................ 65

Fig. 3.15. TEM images of 0.5%Pt/Al-SBA-15; 0.5%Pt/Al-B-SBA-15 and 0.5%Pt/B-SBA-15 . ............................................................................................... 66

Fig 3.16. NH3-TPD curves of 0.5% Pt/Al-SBA-15; 0.5% Pt/Al-B-SBA-15 and 0.5% Pt/B-SBA-15 catalyst. ................................................................................... 66

Fig 3.17. Conversion of n-heptane over the three catalysts of 0.5%Pt/Al-SBA-15; 0.5%Pt/Al-SBA-15 and 0.5%Pt/B-SBA-15. ........................................................... 69

Fig. 3.18. The selectivity of branched heptanes over the investigated catalysts ...... 70

Fig. 3.19. The heptane conversion versus reaction time and temperature over the Pt/M-SBA-15 catalysts (M=Al and/or B) ............................................................... 71

Fig 3.20. The variation of the selectivity to branched heptanes versus reaction time and temperature over the investigated catalysts (Pt/Al-SBA-15 (a), Pt/Al-B-SBA-15 (b), Pt/B-SBA-15 (c) .............................................................................................. 72

Fig 3.21. The yield of the cracked product over the investigated catalysts (300 oC, 12 h) ...................................................................................................................... 73

Fig 3.22. DTA/TGA curves of the investigated catalysts after 24hours reaction time .............................................................................................................................. 74

Fig 3.23. Effect of reaction temperature on the conversion of tetralin over investigated catalysts((A): Pt/Al-SBA-15; (B): Pt/Al-B-SBA-15; (C): Pt/B-SBA- 15). The reaction condition: liquid phase; reaction time: 3 hours ........................... 77

Fig 3.24. Effect of hydrogen pressure on the conversion of tetralin over investigated catalysts ( (A): Pt/Al-SBA-15; (B): Pt/Al-B-SBA-15; (C): Pt/B-SBA-15). The reaction condition: liquid phase; reaction time: 3 hours ......................................... 78

Fig 3.25. The conversion of tetralin and cis/trans ratio over the investigated catalysts ................................................................................................................. 79

Fig 3.26A. TG curves of Pt/ B-SBA-15 (A) after reaction. ..................................... 80

Fig 3.26B. TG curves of Pt/ Al-SBA-15 (B) and Pt/Al-B-SBA-15 (C) catalysts after reaction .................................................................................................................. 81

Fig 3.27. Square wave voltammograms of 10-5M PA at the 1%Pt/M-SBA-15-GPE (where M=Al and/or B) electrodes in 0.1M phosphate buffer (pH=7). ................... 82

Fig 3.28. Low angle XRD pattern of 1%Pt/Al-SBA-15 catalyst ............................. 83

Fig 3.29. Nitrogen adsorption-desorption isotherms at 77K (A) and pore size distribution (B) applying BJH method in the desorption branch of 1%Pt/Al-SBA-15 catalyst. ................................................................................................................. 84

Fig 3.30. TEM image of 1% Pt/Al-SBA-15 catalyst. ............................................. 85

Fig. 3.31. Cyclic voltammograms at Pt/Al-SBA-15-GPE in absence (dot line) and in presence of 7 x 10-5 M of PA (solid line). Inset: CV at unmodified GPE in presence of 7 M of PA. ...................................................................................................... 86

Fig 3.32. Cyclic voltamogramms of 7 x 10-5 M PA at Pt/Al-SBA-15-GPE recorded at different scan rate. Inset influence of scan rate on anodic peak currents intensities at Pt/Al-SBA-15-GPE () and GPE () electrodes (A). ....................................... 87

Figure 3.33. Nyquist plots recorded at Pt/Al-SBA-15-GPE modified electrode () and GPE unmodified electrode () (inset) into a solution containing 1 mM K4[Fe(CN)6]/K3[Fe(CN)6] + 0.1 M phosphate buffer (pH 7). .............................. 88

Fig 3.34. Square wave voltamogramms for different concentration of PA at Pt/Al- SBA-15-GPE modified graphite paste electrode (A) and calibration curve of Pt/Al- SBA-15-GPE modified graphite paste electrode () and GPE () for PA (B). .... 90

Fig 3.35. Square wave voltamogramms recorded at Pt/Al-SBA-15-GPE modified electrode in a presence of a mixture of 7 x 10-6 M paracetamol, 9 x 10-3 M ascorbic acid and 10-6 M uric acid. .................................................................................... 91

xii

Fig 3.36. SWVs (A) and calibration curve (B) for detection of PA from tablets using Pt/Al -SBA-15-GPE modified electrode................................................................. 92

LIST OF TABLES

Table. 3.1. Physicochemical properties of SBA-15, B-SBA-15 and B/SBA-15 samples .................................................................................................................. 52

Table. 3.2. Amonia TPD results of SBA-15; B-SBA-15 and B/SBA-15 ................. 53

Table 3.3. Textual characteristic of SBA-15 and the modified SBA-15 samples. ... 56

Table. 3. 4. Results of EDX analysis ...................................................................... 58

Table 3.5. Acidic properties of Al-SBA-15; Al-B-SBA-15; B-SBA-15 samples according to NH3-TPD ........................................................................................... 61

Table. 3.6. Surface area and pore size of catalysts and the corresponding supports .............................................................................................................................. 64

Table. 3.7. Results in NH3-TPD of catalysts .......................................................... 67

Table 3.8. Conversion of n-heptane over the Pt/M-SBA-15 (M=Al and/or B) catalysts ................................................................................................................. 69

Table. 3.9. Coke content determined from the thermogravimetry analysis of the investigated catalysts after a 24 hours reaction time ............................................... 74

Table 3.10. Tetralin conversion and selectivity of products .................................... 79

Table 3.11. Surface area and pore size of Al-SBA-15 support and 1%Pt/Al-SBA-15 catalyst .................................................................................................................. 84

Table 3.12. The electrochemical parameters of the Pt/Al-SBA-15-GPE electrode material. ................................................................................................................. 86

Table 3.13. Slope of log I versus log v dependence. ............................................... 88

Table 3.14. EIS fitting parameters for Pt/Al-SBA-15-GPE modified electrodes. .... 89

xiii

Table 3.15. Determination of PA from pharmaceutical tablets using Pt/Al-SBA-15- GPE modified electrode ......................................................................................... 93

INTRODUCTION

During the last two decades, the synthesis of mesoporous materials is one of the

most attractive and successful achievements in material science and catalysis. In many

publications of mesoporous material, SBA-15 (Santa Barbara Amorphous) material is

the most frequently studied due to its interesting properties, such as high surface area,

large pore size, thick wall and high thermal stability. However, the lack of acidity

hinders applications of SBA-15 material as catalyst. The ordered mesoporous material

SBA-15 was first synthesized in 1998, since then the functionalization and

modification of this material has attracted much attention and opened many new

applications not only in optics, sensing, adsorption, drug delivery but also in catalysis.

In general, most studies focus on the substituting of the Si atoms or grafting new

functional groups towards its application as photocatalyst, acidic catalyst or catalyst for

oxidation, enzyme immobilization,…

Recently, the growing energy crisis, living standard and population led to the

increasing demand for the petroleum fuels. It is essential to produce fuels with

enhanced quality to increase combustion efficiency and reduce the generation of

pollutants, such as particulate matter (PM 2.5) and photochemical smog. For this

purpose, the hydroisomerization of n-alkanes to branched isomers with high octane

number has received much attention. The increase of octane number of produced

gasoline by hydroisomerization is very different from that of the conventional fluid

catalytic cracking (FCC) because FCC’s gasoline is rich of olefins and aromatics which

generate big amount of PM 2.5 and photochemical smog due to their incomplete

combustion. To meet the demand for high quality diesel fuels, the hydrogenation of

polynuclear aromatic hydrocarbons (PAHs) is also an important process to produce

good performance diesel fuel with low aromatic content. PAHs are undesired

compounds which generate emissions of undesired particles in exhaust gases and

decrease the cetane number of diesel.

The hydroisomerization of n-alkanes and the hydrogenation of PAHs have often

been investigated over bifunctional catalysts which have metal sites for

hydrogenation/dehydrogenation and acid sites for isomerization. Catalytic activity,

stability and selectivity,… of these catalysts depend on the characteristics of the acid

sites and metal sites, on the metal-acid functions balance. The previous researches

showed that noble metal (such as Pt, Pd) are the most used metals for supplying metal

sites due to their strong hydrogenation activity and high stability. In many reported

researches, to improve the catalytic performance of the hydroisomerization and the

hydrogenation, various supports as metal oxides, zeolite (Y, beta, mordenite, ZSM-5),

silicoaluminophosphate, carbides of transition metal, pillared clays or mesoporous

materials (MCM-41) have been investigated. However, the high conversion usually

leads to low selectivity to branched isomers. The Bronsted acid sites increased cracked

products and micropores limited the diffusion of isomers to the bulk phase prior to

consecutive undesired cracking reactions. In Viet Nam, isomerization of n-alkane has

2-, Pt/WO3-ZrO2/SBA-15,

been studied over many catalysts such as MoO3/ZrO2-SO4

Pt/Al2O3, Pd/HZSM5 catalysts promoted by Co, Ni, Fe, Re,…. However, most of

studies were performed at the mild condition without hydrogen pressure…

For SBA-15 material, the mesopores structure exhibits the good mass transfer

and allows the diffusion of large reactants to the surface. The substitution of Si by Al,

B generates the acid sites. Moveover, the previous studies showed that boron promoter

could decrease the coke formation and improve the catalyst stability.

From above mention, in order to exploit the attractive structure properties of

mesoporous SBA-15 material, the bifunctional catalysts based on Pt/SBA-15 modified

with Al and B were chosen for the dissertation. The effect of heteroatom nature on the

acidic properties of modified M-SBA-15 supports and bifunctional 0.5% Pt/M-SBA-

15 catalysts (where M = Al-, B- or Al-B-) were studied. The catalytic activity of the

investigated catalysts in n-heptane hydroisomerization and tetralin hydrogenation were

discussed.

In electrochemistry, the SBA-15-based materials recently have been attractive

compounds used for the chemical modification of electrode surfaces. The mesoporous

structure is likely to impart high diffusion rate of target species. The uniform

mesostructure, high surface area of SBA-15 could improve the electroactivity of

modified electrode.

On the other hand, platinum is a noble metal which has good activity, high

electrical conductivity, reproducibility at electrochemical conditions. Platinum

nanoparticles have also been widely employed as modifiers for electrochemical

detection of organic molecules. Therefore, platinum nanoparticles supported on

modified mesoporous material can be considered as electrochemical catalysts to

improve the performance of sensoring processes.

Paracetamol is an analgesic and antipyretic agent extensively recommended for

treating pain and fever. In the case of overdose, the accumulation of its toxic

metabolites may cause kidney and liver damage. Therefore, the determination of

paracetamol have received much attention. In this dissertation, the 1% Pt/M-SBA-15

catalysts (where M = Al-, B- and Al-B-) were synthesized and their applicability in the

electrochemical detection of paracetamol were also studied.

The objective of the study

The purpose of the thesis is to synthesize the effective catalysts based on

Pt/SBA-15 modifed with Al and/or B and their applicability in n-heptane

hydroisomerization, tetralin hydrogenation and paracetamol detection.

The scope of the research is to:

- Synthesize M-SBA-15 materials and the corresponding (0.5%; 1%) Pt/M-SBA-

15 catalysts (where M = Al-, B- or Al-B-).

- Investigate the effect of heteroatom nature on the acidic properties of

modified M-SBA-15 supports and bifunctional 0.5% Pt/M-SBA-15 catalysts (where M

= Al-, B- or Al-B-).

- Investigate the applicability of these catalysts in n-heptane hydroisomerization,

tetralin hydrogenation .

- Investigate the applicability of 1% Pt/M-SBA-15 catalysts in electrochemical

detection of paracetamol using chemically modified electrodes.

THE NEW CONTRIBUTION OF THE DESSERTATION

The effect of Al and B incorporated SBA-15 support on the acidic properties

and catalytic activity of the supported Pt/M-SBA-15 (where M = Al-, B- and Al-B-)

catalysts have been investigated. The obtained results contributed to knowledge about

the influence of acidic support on the performance of bifunctional catalysts.

The investigated bifunctional catalysts have been applied in the

hydroisomerization of n-heptane and the hydrogenation of tetralin at the reaction

condition of liquid phase, hydrogen high pressure. These results showed their potential

application in industrial catalytic processes.

Chemically modified electrodes based on an ordered mesoporous structure

incorporating Pt nanoparticles (Pt/Al-SBA-15-GPE electrode) were prepared,

characterized and applied for the detection of PA. The well-obtained values for the

analytical parameters (sensibility, limit of detection, linear range, no interference)

could recommend the potential application of this composite electrode materials for

identifying PA in real samples.

CHAPTER 1. LITERATURE REVIEW

1.1. Mesoporous material and ordered mesoporous silica SBA-15

According to IUPAC nomenclature, mesoporous materials are materials which

have pore sizes between 2 and 50 nm. The researchers of Mobil Oil Corporation

introduced the first family of mesoporous silica materials M41S in 1992. These

materials have received much attention due to their high surface area and uniform pore

size 2-10nm [1]. Types of different structures were obtained depend on the different

used synthesis conditions such as hexagonal MCM-41, cubic MCM-48, laminar phases

MCM-50. The interaction between templates and inorganic species affects the structure

of obtained materials.

The ‘liquid crystal mechanism’ of MCM-41 which was suggested by J.S. Beck

et al. [2] was illustrated in Fig 1.1.

Fig 1.1. Formation mechanism of MCM-41 suggested by Beck et al [2]

Spherical micelles assemble in hexagonally ordered cylindrical micelle when

the silica precursor is added. Silica condensation around ordered micelles makes the

silica walls. The templates are removed in calcinations to give the porous ordered

materials.

In 1998, Stucky and coworkers reported a new mesoporous silica material SBA-

15 (Santa Barbara Amorphous) through using nonionic copolymers as organic structure

directing agents. SBA-15 has the hexagonal structure with ordered mesopores up to

50nm, high surface area (600-1000 m2/g) and thick pore wall (3-6nm) [3]. These

characters enhance SBA-15 thermal and hydrothermal stability compared with MCM-

41. Beside the uniform mesopore, SBA-15 has micropores in the mesopore walls.

These micropores interconnect hexagonally ordered mesopores in SBA-15 structure.

The formation mechanism of SBA-15 is similar to the formation of MCM-41.

Silica precursor, types of template, pH of solution,… are the important factors that

influence the characterization of obtained SBA-15.

Some pure silica sources used for synthesis of SBA-15 are alkoxides such as

tetramethylorthosilicate (TMOS) or tetraethyl orthosilicate (TEOS),…[4]. By using

amphiphilic triblock copolymer as template, the ordered hexagonal SBA-15 was

synthesized in strong acidic conditions (pH=1). When pH is over the isoelectric of

silica (i.e, at pH=2-6) precipitation or formation of silica gel couldn’t occur. At neutral

pH of 7, the formation of disordered or amorphous silica may occur.

1.2. The modified SBA-15 materials and applications

Although SBA-15 has many good properties such as high surface area,

hydrothermal stability,… its applicability in catalysis is limited due to the lack of

acidity. Many efforts which include functionalization of surface and deposition of

active metal on the materials to active the surface and create acid sites have been

carried out. The functional mesoporous materials of SBA-15 have opened many

opportunities for its application in catalysis.

Various methods have been used to modify SBA-15, which includes

functionalization of surface and deposition of active metal on the materials.

i. The functionalization can be proceeded directly (direct synthesis) or

post- grafting. [5][6]

- Direct synthesis: Silica sources (TEOS, TMOS,…) were co-condensed

with organotrialkoxysilane in the presence of different templating agents, as shown in

Fig 1.2. In this way, obtained materials often applied for the adsorption of heavy

metals such as mercury, lead,…

Fig 1.2. Co-condensation approach for the functionalization of mesoporous materials

[5,6]

- Post-grafting: In this method, the reaction between organosilane with

silanol group occurred using solvent under reflux condition. After that, covalent

attachment of functional groups was formed on surface of material.

Fig 1.3. Functionalization of SBA-15 through post-grafting [5][6]

ii. Deposition of active metal to SBA-15 includes metal incorporation, ion

exchange, incipient wetness impregnation.

- Metal incorporation method: the metal precursors are added during

synthesis process. Metal atoms are incorporated into the framework or dispersed on the

surface. The direct- introduction of heteroatoms into framework of SBA-15 is difficult

because metal ions are created easily under strong acidic hydrothermal condition.

- Incipient wetness impregnation: a metal salt solution is added to the

support corresponding to the pore volume of the support. The obtained material is dried

and calcined.

Due to the attractive structure properties, after functionalization with active

species on the surface of material, SBA-15 has been the subject of numerous

investigations, i.e., oxidative transformation of hydrocarbons [7,8], reduction processes

[9], Knoevenagel reactions [10], waste water treatments [11,12] and carrier

applications in drugs-delivery [13].

Heteroatoms with valence lower than silicon, such as Al, Fe, Cr, B,…

introduced into framework of SBA-15 creates negative charges [14–17]. Acidity of

modified SBA-15 was generated due to compensating negative charges by protons

[14,15]. The incorporation of Al and B in the framework of SBA-15 to modify its

acidity has been reported. Aluminum incorporation in the SBA-15 framework creates a

large numbers of Bronsted and Lewis acid sites on the surface of mesoporous material.

Bronsted acid sites of mesoporous materials containing aluminum are created by

bridging hydroxyl groups, as illustrated in Fig 1.4.

Fig 1.4. Formation of Bronsted acidic site in mesoporous materials [14]

According to Chen et al. [15,18] boron remains at tetrahedral boron sites in B-

SBA-15 framework. This site can flexibility transform between trigonal and tetrahedral

coordination.

Fig 1.5. Two different tetrahedral structures of boron in B-SBA-15 framework [15,18]

The studies of Grieken [17] and Szczodrowski [19]showed a significant enhance

of acidity of Al-SBA-15 compared to parent SBA-15 support or B-SBA-15. The

modified SBA-15 provided a better dispersion of active species as compared to the

pure SBA-15 and alumina supported catalyst [20]. The bifunctional catalysts

containing noble metal nanoparticle and acidic ordered mesoporous M-SBA-15

showed good catalytic activities for the hydroisomerization of n-dodecane [21], the

hydrogenation of anthracene [21], the hydrocracking/hydroisomerization of

alkanes[22].

In electrochemical applications, chemically modified electrodes based on SBA-

15 derivatives offer attractive features likely to be exploited, such as the increase of

mass transport, rapid electron transfer, easy to develop and good analytical parameters.

In Viet Nam, the modified and functionalized SBA-15 material has been

received much attention by scientists at Institute of Chemistry – Vietnamese Academy

of Science and Technology, VNU University of Science, HaNoi University of Science

and Technology, Ha Noi University of Mining and Geology, University of Science –

Hue University, Quy Nhon Universtiy, Ho Chi Minh city University of Technology,...

The available publications of Vietnamese research teams have summerized as follow:

- Functionalization of SBA-15 with 3-mercaptopropyl trimethoxyxilane for

adsorption of Pb2+ [23]; Schiff-base groups for Suzuki cross-coupling reaction [24]

- Metal incorporation into SBA-15 framework: Fe-SBA-15 for the oxidation of

phenol red reaction [25]; synthesis and characterization of Al-SBA-15 [26], Ti-SBA-15

[27].

- Metal, metal oxide, mixed oxides supported SBA-15 as Ti containing SBA-15

- Hybrid mesoporous SBA-15 for inmobilization onto SBA-15 of enzyme [28]

for photocatalytic oxidation of phenylsulfophtalein [29]; Cu/SBA-15 for oxidation of

styrene [30] and oxidation of LPG [31]; VOx/SBA-15 for oxidative dehydrogenation of

n-butane; WO3/ZrO2 supported on SBA-15 for n-heptane isomerization [32].

1.3. The hydroisomerization of n-alkane over bifunctional catalysts

The hydroisomerization of n-alkanes has played an crucial role in the modern

petroleum industry to produce green gasoline and diesel with high quality, low content

of olefins and aromatics [35, 36].

Fig 1.6. Scheme of n-alkane hydroisomerization over bifunctional catalysts [35]

Typically, the hydroisomerization of n-alkanes takes place over bifunctional

catalysts which have metal sites for hydrogenation/ dehydrogenation and acid sites for

isomerization. The general scheme of n-alkane hydroisomerization is shown in Figure

1.6.

The classical isomerization mechanism contains consecutive steps. First, the

dehydrogenation of n-alkanes is catalysed by platinum sites generating the

corresponding n-alkenes. After the protonation of n-alkenes on acid sites, the created

carbenium ions were rearranged and followed by deprotonation on acid sites and

hydrogenation into i-alkanes on metallic sites [36–38]. The hydrocracking reaction

always takes place during the hydroisomerization of n-alkane because the iso-alkenes

intermediates suffer the bond cracking of C-C on acid sites, thus that reduces the yield

of the branched hydrocarbon. Accordingly, a metal–acid balance of the bifunctional

catalysts is necessary to achieve a high hydroisomerization activity and a limitation of

the cracking reaction.

1.3.1. Metal function of bifunctional catalysts

The transition metals as Pt, Pd, Re, Ir, Ni, Co,… have been employed for

providing metal sites of bifunctional catalyst [39]. Among these metals, catalysts

loaded with Pt or Pd are the most used metal sites in the industrial application of n-

alkane hydroisomerization due to their strong hydrogenation activity and high stability

[40]. The previous researches showed the metal loading at the range of 0.4 – 0.6%

which revealed the good acid – metal balance of bifunctional catalysts. In many metal

loading methods, precipitation and impregnation are main methods used in industry

[41].

The effects of different platinum precursors as Pt(NO3)2, H2PtCl6, PtCl4,

Pt(NH3)4Cl2 and (NH4)2PtCl4 on catalytic behaviors of Pt/ZSM-22 catalysts were

investigated by Wang et al. The results of Wang [34] showed that the H2PtCl6

precursor presented the highest metal dispersion while the Pt(II) precursors produce

larger Pt particles. Therefore, the prepared H2PtCl6 catalysts demonstrated higher

catalytic behaviors. It is also found that in the presence of hydrogen, the Pt sites can

hydrogenate coke precursors maintaining the stability of the catalyst [42, 43].

Recently, the use of a second metal in the synthesis of bimetallic bifunctional

catalysts has been investigated. Yang and Woo [44] studied the hydroisomerization of

n-heptane using the Pt-Ir/NaHY and Pt/NaHY catalysts. The results showed that the

higher behavior was realized and the coke formation decreased over Pt-Ir/NaHY

catalyst compared with that of Pt/NaHY catalyst.

In the researches of Bauer et al [45], the Pt-Pd/zeolite beta catalysts were

prepared and tested for the n-hexadecane hydroisomerization. The investigated

catalysts demonstrated a larger dispersion of bimetallic sites due to the intimate

interactions between two metal components and their similar lattice constants. So that

the bimetallic bifunctional catalysts revealed the higher catalytic activity compared

with monometallic ones.

Eswaramoorthi and Lingappan [46, 47] reported the hydroisomerization of n-

hexane and n-heptane using Pt-Ni/SAPOs (SAPO-5 and SAPO-11) catalysts. The

results indicated that introduction of Ni led to the modification of the metal-acid

balance due to the increase of the bimetallic sites dispersion and covered acid sites.The

best yield of isomer products was obtained over the optimum catalyst containing Pt of

0,2 % and Ni of 0,4 %.

1.3.2. Acid function of bifunctional catalysts

Acid function of bifunctional catalysts for the hydroisomerization process are

provided by supports typically including metal oxides, zeolite (Y, beta, mordenite,

ZSM-5). In the recent researches, many materials, such as silicoaluminophosphate,

carbides of transition metal, pillared clays or mesoporous materials (MCM-41,

modified SBA-15) have been used as a support. In general, the researches aim to adjust

the acid strength or the structure of the catalyst to get the metal-acid balance although

that is too hard to be reached [48].

1.3.2.1. Bifunctional catalysts with amorphous inorganic oxides

Alumina or amorphous silica-alumina (MSA) are supports used for the first

commercial catalysts of n-alkane isomerization. Corma et at [49] studied the

hydroisomerization of n-decane, n-hexadecane over the Pt/MSA catalysts. The results

showed that the best selectivity in hydroisomerization of n-hexadecane obtained over

the 0.6% Pt/MSA catalysts. Calemma et al [50] also studied Pt/MSA catalysts for the

hydroisomerization of n-octacosane, n-hexatricosane, n-tetra-tetracosane. All catalysts

presented the isomerization yields lower than 65% and the yield decreases with

increasing the length of the n-alkane chain.

1.3.2.2. Bifunctional catalysts with super acid solids

The Pt/SO4/ZrO2 and Pt/wO3/ZrO2 catalysts were studied in the

hydroisomerization of n-hexadecane by Wen et al and Keogh et al. [51]. They showed

the very high acidity, thus the isomerization selectivity was low even at low

conversion. In the presence of hydrogen, 80% of n-hexadecane was cracked over

Pt/SO4/ZrO2 catalysts at 150 oC. These catalysts also revealed a low stability at high

temperature [52].

1.3.2.3. Bifunctional catalysts with zeolite support

Zeolite possesses acidic sites on high surface area, large pore volume, high

adsorption capacity, thus the bifunctional metal supported zeolites favored for

hydroisomerization. The acidity of zeolites is generally very strong because they

usually possess strong Bronsted acid sites. Accordingly, the strong cracking activity

reduces the yield of isomer products especially for the hydroisomeization of long chain

n-alkanes.

Park et al [35] studied the hydroisomerization of n-hexadecane over

bifunctional catalysts containing zeolite supports as ZSM-5, ZSM-22, Y, Beta at 350oC

and 103 bar. It was found that the catalytic activity depended on the acid strength of

catalysts. The conversion was in the range of 37 – 45 wt%. The Pt/Y catalyst showed

the isomer selectivity of 15.6-75.7% .

On the Pt (0.3%)/ZSM-22 catalyst, Claude et al. [53] investigated the

hydroisomerization of long-chain n-alkanes (n-decane to n-tetracosane). The results

showed the improving yield of total isomers. The maximum obtained yield was at 77-

90%.

In some recent researches, the weakening of zeolite acidity has been considered

as an effective route to enhance zeolite-based bifunctional catalysts performances. The

changing of the ion-exchange solutions and the mixing of acid supports with additional

chemicals with weaker acidity are the most selected ways to decrease the Bronsted

acidity of zeolite. Wang et al. [54] used the NH4NO3/(NH4)2SiF6 mixture as the ion-

exchange solution instead of NH4NO3 to modify ZSM-22 support. When studying the

hydroisomerization of n-dodecane, the yield of i-dodecane increased from 38.8% to

77%. Zhang et al. [55] studied the hydroisomerization of n-hexadecane over the Pt/Eu-

1-ZSM-48 catalyst. The obtained yield of i-hexadecane over Pt/Eu-1-ZSM-48 catalyst

was higher than that over Pt/Eu-1 or Pt/ZSM-48 catalysts due to the combination of the

large Bronsted acid density of Eu-1 and the mild Bronsted acid strength of ZSM-48.

1.3.2.4. Bifunctional catalyst with silicoaluminophosphases (SAPO-n) acid supports

Beside zeolite, zeolite like silicoaluminophosphate (SAPO) materials are the

important molecular sieve materials used in hydroisomerization. The SAPO-n supports

(n=11, 31 or 41, respectively) generally have weaker acidity than zeolites [54, 56].

Acid Bronsted sites of SAPO-n were formed due to the substitution of Al or/and P

atoms by Si atoms and had strong effects on catalytic behaviour. The bifunctional

catalysts based on Pt/SAPO-n have been reported.

The Pt (1%)/SAPO-n (n = 11, 31 or 41) catalysts were used for the

hydroisomerization of n-octane at the temperature range of 200-400oC, under

atmospheric pressure [56]. The results showed that the hydroisomerization reaction rate

was controlled by the diffusion. The activity of investigated catalysts were reduced in

the order SAPO-41> SAPO-11> SAPO-31 because the acid sites and acid strength of

SAPO-41 and SAPO-11 were higher than that of SAPO-31.

The hydroisomerization of n-hexane, n-octane and n-hexadecane over

Pt(0.5%)/SAPO-11 and -31 has been studied by Sinha et al [57]. The investigated

catalysts showed the most reactive only for n-hexadecane while the least reactive was

obtained for n-hexane. These results demonstrated the Pt/SAPO-n catalysts were

suitable for long-chain n-alkane hydroisomerization.

Kim et al. [58] found that the consecutive cracking reactions could be prevented

by reducing the external Bronsted acid sites, thus the catalytic performance of

Pt/SAPO-11 would be enhanced. A series of hierarchical SAPO-11 were synthesized

by using various templates as methyloctadecyl (ST-SAPO-11) or carbon (C-SAPO-11).

In the case of using methyloctadecyl template, Bronsted acid sites were mainly located

at the outer surfaces of SAPO-11 crystals. In contrary, most of Bronsted acid sites still

locate in the microporous channel when using carbon templates. The internal Bronsted

acid sites facilitate the isomerization while the consecutive cracking reaction is

catalysed by the external Bronsted acid sites. Accordingly, the results of the n-

dodecane hydroisomerization showed higher yield of i-dodecane over Pt/C-SAPO-11

than that over Pt/ST-SAPO-11 catalyst.

1.3.2.5. Bifunctional catalysts with mesoporous materials

Mesoporous materials (such as MCM-41 and SBA-15) exhibit very good

properties for mass transfer due to their mesoporousity. These materials possess the

wide pore diameter, high surface area and the thermal stability affording a diminution

of the diffusion limitations for branched alkanes isomers [59, 60]. The substitution of

Si by Cr, La, Ce, Zn, B, Fe, Ga, Ti, V, Sn or Al, B led an increase of the activity and

stability [61, 62]. Noble metals (Pt or Pd) dispersed on Al-MCM-41 [63] or Al-SBA-15

[64, 65] showed a high activity for hydroisomerization. By using hydrothermal

procedures, P. T. Huyen et al. synthesized Al-SBA-15 and ZSM-5/SBA-15 (ZSC)

composite. These supports were loaded by 0.5% Pt and investigated in the

hydrocracking/hydroisomerization of n-decane. The Pt/Al-SBA-15 catalyst with

merely Lewis acidity was active for hydroisomerization while Pt/ZSC was suitable for

hydrocracking due to its strong Bronsted acidity [22]. Y. Zhang et al. [60] synthesized

the micro/mesoporous Y/MCM-41 composite and studied the influences of the

mesoporous MCM-41 on catalytic activity of the Pt-loaded Y/MCM-41 catalyst in the

n-decane hydroisomerization, where Y/MCM-41 support was the composition of

mesoporous MCM-41 and zeolite Y. The investigated catalysts showed the high n-

decane conversion, the good selectivity to mono-branched isomers compared with that

of Pt/Y catalyst. The mesoporous MCM-41 presence improved the metal-acid balance

and reduced the diffusion limitation to large molecules, thus corresponding positive

effects to the performance of Pt-loaded Y/MCM-41 catalyst.

In summary, an ideal bifunctional catalyst for the n-alkanes hydroisomerization

should achieve high isomerization selectivity simultaneously with the least formation

of cracked products. It was necessary to reach the balance between acidity and

hydrogenation activity and the proper pore channel for the enhancement of catalytic

performance. Hence, beside metal function, textural properties of support, pore size,

surface area, acidity,… are crucial parameters of bifunctional catalysts.

In the researches of n-alkanes hydroisomerization over bifunctional catalyst,

SAPO-n and zeolites are the most studied acid supports. Catalysts containing these

supports showed an improvement of catalytic performance due to their acidity and

porous structure. They also exhibited a very high sensitivity to H2O, S in the feedstock

and eliminated the corrosion, that solved the limitation of the chlorinated Al2O3

catalysts. However, the catalytic conversion over Pt/zeolite catalysts was not

sufficiently high simultaneously with high selectivity to branched isomers. The

Bronsted acid sites increased cracked products and micropores limited the diffusion of

isomers to the bulk phase prior to consecutive undesired cracking reactions.

Isomerization of n-alkane has been studied by many scientists in Viet Nam.

Research teams of VNU University of Science studied isomerization of n-hexane and

2-[66], Pt/WO3-ZrO2/SBA-15 [32] catalysts. The teams

n-heptane over MoO3/ZrO2-SO4

of HaNoi University of Science and Technology reported the isomerization of n-

hexane over Pt/Al2O3 catalyst [67]. n-hexane hydroisomerization over Pd/HZSM5

catalysts promoted by Co, Ni, Fe, Re were investigated by scientists at Ho Chi Minh

City University of Technology [68]. However, most of studies were performed at the

mild condition without hydrogen pressure…

From above contents, the mesoporous materials showed potential supports for

bifunctional catalyst of hydroisomerization. For SBA-15 material, the substitution of Si

by Al, B generates the acid sites which acted as the acidic sites of bifunctional catalyst.

The mesopores exhibit the good mass transfer and allow the diffusion of large reactant

to the surface. Therefore, in this thesis, the effect of heteroatom nature on the acidic

properties of Pt/M-SBA-15 (where M = Al-, B- and Al-B-) and the catalytic activity

on n-heptane hydroisomeriation were studied.

1.4. Hydrogenation of polynuclear aromatic hydrocarbon (PAHs)

1.4.1. Hydrogenation of polynuclear aromatic hydrocarbon (PAHs)

Hydrogenation of PAHs has been applied to upgrade quality of heavy fuels and

increase cetane number (CN) of diesel. LCO (light cycle oil) from fluidized catalytic

cracker (FCC) contains an appreciable number of PAHs. They caused negative

influences on diesel fuel due to their low CN, high density and the generation of

undesired particles in emissions. Therefore, hydrogenation of PAHs has been studied

up to now.

PAHs hydrogenation is a complex process taking place in consecutive steps.

Hydrogenation activity increased with the number of aromatic rings in molecules [69].

The hydrogenation of the first rings in PAHs molecule was easier than the

hydrogenation of the last remaining ring. In the heavy fuels, tetralin is one of the

typical PAHs. So it was often selected as a model compound to study in PAHs

reaction.

Fig 1.7. Stepwise hydrogenation of an adsorbed tetralin molecule to cis- and trans-

decalin [70]

Hydrogenation pathway of tetralin has been reported. Williams et al.[70]

proposed the pathway of tetralin hydrogenation as illustrated in Figure 1.7.

Tetralin was hydrogenated in sequential steps via 9,10_ and 1,9_octalin to cis-

and trans-decalin. The pathway which proceeds through 1,9_octalin is the main

reaction way.

Sato et al. [71] studied reaction mechanisms of tetralin hydrocracking over

NiW/USY zeolite catalysts. Reaction network of tetralin hydrocracking is illustrated in

Fig 1.8. The obtained products were classified into 3 groups: (i) cis-decalin and trans-

decalin as hydrogenation products; (ii) isomerization, hydrogenolysis, hydrocracking

products that include 2- methylindan, n-butylbenzene, iso-butylbenzene, and volatile

compounds…, (iii) naphthalene.

Fig 1.8. Reaction network of tetralin hydrocracking [71]

The similar products of tetralin hydrocracking are obtained. Bifunctional

catalysts presented higher activity than metal-catalysts in PAHs hydrogenation reaction

[72–74]. Beside the hydrogenation on metal sites, the acid sites of the support also

participate in the hydrogenation reaction [75, 76]. Composition of products depend on

metal activity and acidity of supports.

Fig 1.9. Cetane number (CN) of some possible products of naphthalene hydrogenation

(CN values according to Santana et al [79]).

Fig 1.10. Reaction scheme for the selective hydrocracking of tetralin into BTX [78]

Ferraz et al. [77] researched hydrogenation, hydrocracking of tetralin and its

reaction intermediates using NiMo catalysts supported on alumina, silica-alumina, and

alumina Y- zeolite. Cetane number of some possible products were reported (Fig 1.9).

Cetane Number (CN) values in Fig 1.9 show that CN of product enhance

significantly if aromatic saturation followed by selective ring opening of naphthenic

structures.

Selective hydrocracking of tetralin for light aromatic hydrocarbons was studied

by Lee et al. [78] over Ni/Ni-Sn/CoMoS catalyst supported on H-Beta (Fig 1.10). The

results showed that H2/tetralin molar ratio lower than 4 increases naphthalene and C9+

aromatic in product. The high selective hydrocracking of tetralin into BTX was

achieved at H2/tetralin molar ratio higher than 4.

To summarize, the available ways to upgrade polynuclear aromatic fractions to

fuels are aromatic saturation; mild hydrocracking and aromatic saturation followed by

selective ring opening of naphthenic structures. Although these routes lead to

significant product quality enhancement, they suffer from several disadvantages.

Hydrocracking leads to significant yields in gasoline-range products, aromatic

saturation is characterized by a relatively high consumption of hydrogen with only

limited improvement of product quality in terms of density and cetane properties, while

the combination of the two approaches leads to higher improvements of product quality

but it requires a very high hydrogen consumption which strongly affects the economics

of the process. An alternative upgrading route consists in partial polyaromatic

compound saturation to produce less condensed structures.

1.4.2. Catalysts for PAHs hydrogenation

1.4.2.1. Catalysts for upgrading polynuclear fractions.

The hydrogenation of PAHs has been studied extensively using different

catalysts such as solid acidic catalyst; metal/acidic support catalysts; metal/non-acidic

supports; homogene ous catalysts.

- Solid acidic catalysts:

Chareonpanich et al [80] used USY-zeolite for thermal cracking at 600oC, total

yield of benzene, toluene, xylene, and light hydrocarbons (methane, ethane, propane)

obtained approximately 100%. Coke and tar were not detected. Mechanism showed

that hydrocracking of diphenylmethane, n-butylbenzene, and tetralin were formed by

hydrocracking of C-C bond. Hydrogenation of aromatic ring was the first step and

hydrocracking reaction was the subsequent step. In the case of 1-methylnaphthalene,

aromatic ydrogenation took place prior to hydrocracking of methyl group.

Hydrocracking of anthracene and phenanthrene trend to crack at outer rings.

Yue et al [81] studied new catalysts impregnated on active carbon, included

pentachloro antimony, trimethylsilyl trifluoro-methane sulfonate, isometric

pentachloro-antimony. The results revealed that CAr-Calk bond of di(1-naphthyl)

methane could be cracked to naphthalene and 1-methylnaphthalene on the catalyst at

300oC under hydrogen pressure. The solid acid had higher activity in hydrocracking

reaction. H2 was dissociated to non-active H- and active H+. Step of attaching active

H+ to iso site of di(1-naphthyl) methane was the deciding step of hydrocracking

process.

- Catalyst of metal/acidic support.

Matsuhashi et al. [82] examined hydrocracking reaction over Pt/Al2O3 catalyst

which was synthesized by impregnation method. The influences of synthesized

condition on dispersion as well as the influence of dispersion on reaction rate were

considered carefully. This research showed that reactivity of catalyst was affected by Pt

precursor and the dispersion of Pt impacted well to reaction rate.

Fan et al [83] studied anthracene hydrocracking reaction to ethyl biphenyl over

NiFe/HZM-5 catalyst. In the presence of water, liquid products yield increased and

yield of gas products decreased. Without water and CO2, nitrogen compound would

poison catalyst, gave bad influences on process [84]. Mixture of CO2 and water could

limit that problem and give higher yield if there was no nitrogen compound in the

feedstock. However, some of nitrogen compounds such as pyrrole, pyridine and 2-

methylpyrazine could also enhance the reaction in the presence of CO2 and water.

Calemma et al. [85] reported results of PAHs hydrocracking reaction over Ir and

Pt on various supports such as ZSM-12, super durable zeolite Y (SiO2/Al2O3=200

mol/mol) and zeolite HSZ-390HUA, amorphous mesopore SiO2-Al2O3 and Al2O3-B.

The results exhibit that properties of products depend on characterization of supports

and used metals.

Tailleur et al [86] applied WNiPd/CeY-Al2O3 catalyst for the conversion of

heavy paraffin and aromatics into a high-quality diesel fraction. This research showed

that the presence of two acid strengths that had different affection to paraffin and

aromatics isomerization, ring opening, and cracking reaction. The aromatic adsorption

on acid sites reduces the cracking rate and improves the formation of di- and tri-

branched paraffin.

- Catalyst metal/ non-acidic supports

Haas et al. [87] reported the conversion of cis-decalin at a hydrogen pressure of

5.2 MPa and temperature of 250-410 oC using Ir and Pt/SiO2. On the Ir/SiO2 catalysts,

this reaction started at 250-300 oC. The hydrogenolytic opening of one six-membered

ring to form the direct ring –opening products butylcyclohexane, 1-methyl-2-

propylcyclohexane and 1,2-diethylcyclohexane was the first step. The hydrogenolysis

of endocyclic C-C bond into open chain decanes or exoclyclic C-C bond into methane

and C9 naphthenes. C9 naphthenes could be converted to C9, C10 hydrocarbon by

endocyclic hydrogenolysis.

On the Pt/SiO2 catalysts, the decalin conversion started at higher temperature of

350-400 oC. The products have a large content of tetralin, naphthalene, spiro [4,5]

decane and butyl cyclohexane.

- Homogeneous catalyst:

Guan et al [88] studied 2 stages of residue oil hydrocracking. The first stage

was the hydrogenation at low temperature and the second one was the thermal cracking

at high temperature. Anthracene product was hydrogenated at 416oC using

homogeneous catalyst of FeSO4 and (NH4)6Mo7)O24.4H2O, the conversion of

anthracene reached 51%. However, the used catalyst couldn’t be separated from the

products.

1.4.2.2. Catalysts for tetralin hydrogenation

Tetralin, one of the typical PAHs in heavy fraction, has usually been used as

model compound to investigate the hydrogenation. Tetralin hydrogenation was studied

in liquid phase by Rautanen et al. on Ni/Al2O3 catalyst over a temperature range of 85-

160 oC and a pressure range of 20 - 40 atm. Tetralin was diluted by decane solvent with

the tetralin concentration of 5, 10,15 mol% [89].

Wiliams et al. [70] reported the hydrogenation of tetralin on Pt/Al2O3, Pt/ASA,

Pt/SiO2 catalysts at the condition of 50 atm and 180 oC. The results showed that

Pt/SiO2 has the lowest activity.

Valles et al [90] researched experimental design optimization of the tetralin

hydrogenation over Ir-Pt-SBA-15 at the reaction condition of 15at of hydrogen

pressure, a temperature range from 200 – 220 oC and at 3 h and 5 h of reaction time.

The 1%Ir-0.8%Pt-SBA-15 catalyst showed the best yield to cis-decalin of 74% at the

temperature of 200 oC.

Mouli et al. [91] studied the quality improvement of hydrotreated LGO on

Pt/Al-SBA-15 and Pt/HY catalysts. The results showed that the secondary cracking

products were observed on Pt/HY catalysts, whereas Pt/Al-SBA-15 catalyst was

effective in aromatic saturation without secondary cracking. Thus, cetane number of

products increased strongly over Pt/Al-SBA-15 catalyst while that couldn’t improve

effectively on Pt/HY catalyst.

In the large number of reports, mesoporous materials such as hexagonal

mesoporous silica have been received attention in recent years due to their high surface

area, large pore volumes. Compare with MCM-41 and other supports, SBA-15 material

shows its advantages as large pore diameters ranging, thicker pore walls and better

hydrothermal stability. The incorporation of Al in the framework of SBA-15 creates

the acidity at moderate level which is suitable for the preparation of bifunctional

catalyst.

Therefore, in this thesis, tetralin was chosen as model reactant and the catalytic

behaviors of Pt/M-SBA-15 catalysts (where M= Al and/or B) on tetralin hydrogenation

were studied.

1.5. Overview of paracetamol detection.

1.5.1. Introduction of paracetamol

Paracetamol (PA) or acetaminophen (N-acetyl-para-aminophenol) is a medicine

widely used as an analgesic and antipyretic agent. Its structure is shown in Fig 1.11.

The determination of PA in pharmaceutical formulation has received much attention

because PA is extensively recommended for treating pain and fever. In the case of

overdose, the accumulation may cause kidney and liver damage. So, it is very

important to research/develop methods for detecting paracetamol rapidly and

accurately.

Fig 1.11. Chemical structure of PA

PA

N-acetyl-p-quinoneimine

Fig 1.12. Electrochemical oxidation of PA [65]

Paracetamol has redox properties, and most electroanalytical techniques can be

considered for the determination of paracetamol. The mechanism for paracetamol

oxidation was illustrated in Fig 1.12. PA suffers a redox reaction involving two

electrons and two protons to form N-acetyl-p-quinoneimine [92].

1.5.2. Electroanalytical methods based on using chemically modified electrodes (CMEs) for paracetamol detection.

Various methods are available for determination of paracetamol in

pharmaceutical formulation, such as: optical method, chromatographic methods,

capillary electrophoretic methods [93,94] and electroanalytical methods.

Electroanalytical methods based on using chemically modified electrode have received

overwhelming interest because they have more advantages over the other sophisticated

methods such as: relatively low cost, fast response, simple instrumentation, high

sensitivity, facile miniaturization, and low power requirement.

In electroanalytical methods, a redox reaction is studied in an electrochemical

cell containing an analyte. When an appropriate potential is applied, the reduction or

oxidation of a substance take place at the surface of a working electrode. The potential

related to the redox process and/or the current intensity related to quantitative

properties are measured. Therefore, substances can be selectively detected by

electrochemical methods. The values of the electrochemical parametres provide strong

information involving the concentration, kinetics, and mechanism of reaction in

solutions.

Electrochemistry based on the charge transfer process take place at the interface

between electrode and solution. A general redox process can be described by the

following reaction:

(1.1) Ox + ze- Red

where: Ox is the oxidized species, Red is the reduced species, z is the number of

the electrons involved in the redox process.

An electrochemical cell needs at least 2 electrodes, but most common

electrochemical cells have a three electrodes system:

Working electrode (WE): on which the reaction of interest is occurring, •

electrode’s response is registered

Reference electrode (RE): to provide a stable half-cell potential •

Auxiliary electrode (counter electrode, CE): to close the current circuit in •

the electrochemical cell.

The relationship between electrode potential and concentration of redox species

can be expressed by Nernst equation:

(1.2) E= Eo’ +

where: Eo’ is the normal standard potential of the redox reaction, R is the

universal gas constant (in J/mol K), T is the absolute temperature (in K), z is the

number of electrons involved in the redox reaction, F is the Faraday constant (in

C/mol), Cox and Cred are the concentration of the redox species which are involved in

the charge transfer process.

Some of the most commonly used electrochemically investigation methods are:

cyclic voltammetry (CV) method, square-wave voltammetry (SWV) and

electrochemical impedance spectroscopy (EIS).

1.5.2.1. Cyclic voltammetry (CV) method [95], 96]

In a cyclic voltammetry method, the solution is unstirred. The applied potential

at a working electrode take values from the initial to the final potential (in forward

sense). When the working electrode’s final potential is reached, the potential start to

return to the initial potential (in reverse sense), while the current is recorded. This

inversion from initial to final potential can be repeated as many times as needed.

If a redox system remains in equilibrium throughout the potential scan, the

redox process is said to be reversible (equilibrium requires that the surface

concentrations of Ox and Red are maintained at the values required by the Nernst

equation).

(a)

(b)

Fig 1.13. Cyclic potential sweep (a) and resulting cyclic voltammogram (b) [95, 96]

(a) (b) (c )

Ep (= Epc - Epa) <59.2/n Ep (= Epc - Epa) > 59.2/n in Ipa<

Case of quasi-reversible

system. Case of irreversible reaction Case of reversible The effect of increasing system system irreversibility on the shape of (Ox + ne-→Red).

cyclic voltammograms

Fig 1.14. Cyclic voltammogram of a reversible reaction system (a), quasi-reversible

system (b) and irreversible reaction system (c) [95]

The shape of cyclic voltammograms is different in function of the type of

process occurring at the electrode interface: reversible (a), quasi-reversible (b) and

irreversible (c), as shown in Fig 1.14.

Using the values of anodic and cathodic potential and intensities (Epa, Epc, Ipa,

Ipc) obtained from cyclic voltammograms, it can be evaluated different important

electrochemical parameters.

1.5.2.2. Square ware voltammetry (SWV)

Square-wave voltammetry (SWV) is a powerful electrochemical technique

suitable for analytical application. In SWV method, a waveform consisting from a

staircase potential ramp modified with square potential pulses is applied to the working

electrode. During each square-wave cycle, the current is measured at the end of the

forward pulse and at the end of the reverse pulse. The net current is defined from

differences between forward and reverse current [95, 97].

SWV was used for obtaining the analytical parameters of working electrodes as

Fig 1.15. (a) Scheme of application of potentials of square wave voltammetry method. (b) The response contains a forward (anodic, I(1)), backward (cathodic, I(2)) and net current ΔI [95]

sensibility, limit of detection, linear range, interferences, etc.

1.5.2.3. Electrochemical impedance spectroscopy (EIS)

Electrochemical impedance spectroscopy (EIS), technique is a powerful method

using alternative currents in order to study electrochemical systems perturbed by small

amplitude signal. EIS gives information on the dielectric constant and the barrier

properties at the solution/electrode interface [95, 98].

When there are different phases between potential and current, the impedance

can be divided into a resistive part, R, where the voltage and current are in phase, and a

reactive part, Xc = 1/(ωC), where the phase difference between current and voltage is

90°. The impedance of equivalent circuit is calculated by Ohm’s Law.

(1.3) Z(jω) =

where: φ = φu - φi: the different phase.

On the other hand, impedance depends on frequency (f) and can be split into a

real part (Z’) and an imaginary part (Z”), respectively.

Fig 1.16. The relation of a real part (Z’) and an imaginary part (Z”) in the complex plane.

Z(jω) = Z’-jZ” ; where: Z”= - │Z│sinφ and Z’=│Z│cosφ

EIS investigation is based on the modeling of electrochemical processes

occurring on the solution/electrode interface. An electrochemical system can be

represented by an equivalent electrical circuit, consisting by resistances, capacitances

and impedances, bonded in series or parallel, each of them having a physical meaning.

The simplest and more used equivalent circuit is the so called Randles equivalent

circuit, illustrated in Fig 1.17.

The faradic impedance (Zf) is considered as general impedance composed by

either the series resistance (Rs), and the pseudocapacity (Cs) or the charge-transfer

resistance and the Warburg impedance (Zw), which represents a kind of resistance to

mass transfer. The impedance components (Z’ and Z”) and frequency response of an

electrochemical system are represented by Nyquist plot and Bode plot. Through these

Cdl

Rsol

plots, the EIS parameters of equivalent circuit are determined.

1.5.3. Chemically modified electrodes (CMEs) for PA detection

Recently, CMEs have been extensively studied in sensor development due to

low background current, easy surface renewal, low limit detection and other important

analytical properties.

As defined by IUPAC, a chemically modified electrode (CME) “is an electrode

made of a conducting or semiconducting material that is coated with a selected

monomolecular, multimolecular, ionic, or polymeric film of a chemical modifier and

that by means of faradaic (charge-transfer) reactions or interfacial potential differences

(no net charge transfer) exhibits chemical, electrochemical, and/or optical properties of

the film” [99]

Electrodes are usually chemically modified by one of the following four

approaches [99, 100]:

(1) Chemisorption-adsorption in which the forces involved are the valence

forces of the same kind as those operating in the formation of chemical compounds;

(2) Covalent bonding-linking agents, such as, e.g., organosilanes or cyanuric

chloride, are used to covalently attach from one to several monomolecular layers of the

chemical modifier to the electrode surface;

(3) Composite mixture (e.g., entrapment in a conductive material), when the

chemical modifier is simply mixed with an electrode matrix material, as in the case of

an electron-transfer mediator (electrocatalyst) combined with the carbon particles (plus

binder) of a carbon paste electrode;

(4) Polymer film coating - electron-conductive and nonconductive polymer

films are held on the electrode surface by some combination of chemisorption and low

solubility in the contacting solution or by physical anchoring in a porous electrode. The

polymer film can be organic, organometallic or inorganic.

In this context, the literature presented different chemically modified electrodes

for PA detection, containing conducting polymers (Au/MWCNT/PANI [98], ECP/

CNT-Poly(3-Aminophenol [101], Au/imprinted PANI [102], poly(p-aminobenzene

sulfonic acid/GCE [103], multiwall carbon nanotubes MWCNT-PtNPs composite

carbon paste electrode [104], magnetic microparticles (MPs)/SWCNT/Au [105],

printex 6L carbon nanoballs/GCE [106], MWCNT/GCE [107], Bi - nanoparticles

/Nafion/BDDE [108], carbon paste electrode [101], PtMWCNTs–TX100-CPE [92],

nevirapine/CPE [92], graphene (Gr)–platinum nanoparticles (PtNP) composite

immobilised with Nafion on glassy carbon electrode (GCE) surface [109], graphene-

modified glassy carbon electrodes [110], etc.

Some detailed examples are summarized below.

Noviandri et al. [101] studied voltammetric determination of PA using the

carbon paste electrode (CPE) modified with carbon nanotube (CNT) and poly(3-

aminophenol). Results showed that the oxidation peak of PA occurs at 450 mV vs.

Ag/AgCl (3M NaCl). The modified CPE revealed the oxidation current of paracetamol

was higher than the received current with bare CPE. The best calibration curve was

found in the PA concentration range of 10-5M - 10-4 M. The limit of paracetamol

detection was 1.1 µM.

Kutluay et al. [107] present a modified a glassy carbon electrode (GCE) with

multiwalled carbon nanotubes (MWCNTs) for the selective detection of paracetamol

(PA) in the presence of ascorbic acid (AA), dopamine (DA) and uric acid (UA). The

square wave voltammetry technique was used for the determination of PA in 0.1 M

phosphate buffer solution (PBS) at pH 7. The results showed that the peak currents

10 M to 1.5 × 10-5 M and a detection limit of 9.0 × 10-11 M was obtained.

were proportional to the concentrations of PA with a linear dynamic range of 2.0 × 10-

Ozma et al [92] reported the incorporation of platinum decorated multi-walled

carbon nanotubes (PtMWCNTs) into the carbon paste matrix. The modified carbon

paste electrode was used for PA detection by using cyclic voltammetry and

amperometry. The combination of PtMWCNTs and TritonX-100 (TX100) onto the

surface of electrode enhanced the electroactivity of the sensing matrix for PA

determination with a lower detection limit of (17.71 ± 2.03) × 10-9 M (expressed for

S/N = 3). Using this composite matrix, PA can be detected selectively in the presence

of ascorbic acid (AA), dopamine (DA) and tryptophan (Trp).

In another research, Tanuja et al. [111] used nevirapine drug to modify the

carbon paste electrode. This electrode was applied for the determination of PA in

presence of folic acid via cyclic voltammetric technique. Results showed that the

simultaneous determination of PA in presence of folic acid without any interference is

feasible at nevirapine modified carbon paste electrode. The detection limit of PA and

folic acid were 0.77× 10-6 M and 2.53× 10-6 M, respectively.

Kalambate et al. [109] studied the reduction at glassy carbon electrode (GCE)

surface of a graphene oxide in presence of hexachloroplatinic acid in order to form a

reduced graphene (Gr)-platinum nanoparticles (PtNP) composite. The obtained GCE

was coated with Nafion (NAF) polymer to make the following interface

NAF/PtNP/Gr/GCE. The simultaneous voltammetric determination of PA and

domperidone was researched with NAF/PtNP/Gr/GCE using the adsorptive stripping

square wave voltammetry (AdSSWV). The results exhibited that the linear working

range of 8.2×10-6 M to 1.6 × 10-9 M PA with detection limits (expressed for S/N = 3) of

1.06 × 10-10 M and 4.37 × 10-10 M for PA and domperidone, respectively.

Another study, carried out by Zidan et al. [112], reported a MgB2 microparticles

modified glassy carbon electrode (MgB2/GCE) for the detection of PA in 0.1 M

KH2PO4 aqueous solution during cyclic voltammetry. A significantly current

enhancement by about 2.1 times was obtained in the oxidation process of PA compared

to bare GC electrode. The detection limit of this modified electrode was found to be

30× 10-6 M. The sensitivity is strongly dependent on pH of supporting electrolyte,

temperature and scan rate.

Electrochemical determination of paracetamol using Fe3O4/reduced graphene

oxide based electrode (Fe3O4/rGO-GCE) was reported by a research team of Hue

University – Viet Nam [113]. The investigated electrode material showed a high

surface area of Fe3O4/rGO dispersed by spherical particles of Fe3O4 in nanoscales. A

low detection limit of 0.72.10-6 M and no interference of caffeine, ascorbic acid and

uric acid were obtained.

SBA-15 material is a highly ordered hexagonal mesostructure with thick

uniform walls, good hydrothermal stability and large surface area. The modification of

SBA-15 led to its effective applications in catalysis, such as: photocatalyst, acidic

catalyst for isomerization, catalysis cracking process,…. [14], 16, 113]. Recently

CMEs containing modified SBA-15 material have been reported such as GC/SBA-15-

NH2/Nafion [115], SBA-Is-INH [116], Agm-SBA-15/GC [117], FM-SBA-15, FD-

SBA-15, FT-SBA-15 [118] (where: Is-INH = (Z)-N'-(2-oxoindolin-3-ylidene , Agm=

Ag(NH3)2NO3SBA-15) . These CMEs showed the potential application in recognizing

2-) in water), hydrogen peroxide.

metal ions (Cd2+, Fe3+, multianalytes (Fe3+ and Cr2O7

Sacara et al [115] used SBA-15-NH2 and MCM-41-NH2 to modified glassy

carbon electrodes coated with Nafion to be used for the electrochemical detection of

Cd(II). The SBA-15-NH2 and MCM-41-NH2 modifiers showed good impact on the

detection limit of metal ions due to their large surface area and adsorption properties.

The GC/SBA-15-NH2/Nafion electrode performed the best results at pH=6 with

sensitivity of 1.52 A/M and limit of detection 0.36× 10-6 M.

Lashgari et al [116] prepared SBA-Is-INH electrode through the

functionalization of mesoporous silica SBA-15 material with a fluorescent

chromophore, (Z)-N'-(2-oxoindolin-3-ylidene) isonicotinohydrazide. It was revealed

that SBA-Is-INH was able to detect two ions with opposite charges, i.e. Fe3+ and

2- over a wide range of pH. The mesoporous structure of SBA-15 are beneficial

Cr2O7

for facilitating the entering and diffusion of target species. This SBA-15 matrix is

optically transparent in the visible region and favorably biocompatible. The limits of

2- were 6.04 10-7 M and 5.09 10-7 M, respectively.

detection of Fe3+ and Cr2O7

In another study carried out by Lin et al [117], 3-aminopropyltrimethoxysilane

(APTMS), then formaldehyde and further Ag(NH3)2NO3SBA-15) were used for

modifying SBA-15. The Ag-mSBA-15 modified electrode (Ag-mSBA-15/GC) was

obtained with silver nanoparticles on the surface showing an excellent electrocatalytic

activity toward the reduction of hydrogen peroxide (H2O2). The uniform

mesostructures, high surface areas, and tunable pore sizes of SBA-15 improves the

electroactivity of the Ag-mSBA-15 modified electrode. The linear range of 48.5 μM–

0.97 M with a detection limit of 12 μM (S/N = 3) were obtained.

On the other hand, platinum is a noble metal which has good activity, high

electrical conductivity, reproducibility at electrochemical conditions. Platinum

nanoparticles have also been widely employed as modifiers for organic molecules

[104, 118]. The above conservations showed that platinum nanoparticles supported on

modified mesoporous material (Pt/M-SBA-15 where M=Al and/or B) can be used as

electrochemical catalysts to improve the performance of sensoring processes.

Therefore, in this thesis, the 1% Pt/M-SBA-15 catalysts (where M=Al and/or B) were

synthesized and their applicability in the electrochemical detection of paracetamol was

studied.

1.6. Conclusions

The hydroisomerization of n-alkanes to produce branched alkanes with high

octane number and the hydrogenation of poly aromatic hydrocarbons to upgrade the

poly nuclear aromatic fraction to fuels are important processes in the petroleum

industry. These processes require the presence of bifunctional catalysts which consist

of a hydrogenation/ dehydrogenation function provided by a metal, and an

isomerization/cracking function provided by a support. Bifunctional catalysts

containing noble metal (Pt or Pd) and supports of amorphous or mixed oxides (Al2O3,

2-), zeolites (Y, Beta, mordenite, ZSM-5) and mesoporous

SiO2-Al2O3, ZrO2/SO4

materials (MCM-41) have been largely reported. The activity, product selectivity of the

catalyst not only depend on acid and metal site densities but also on their proper

balance. However, the functions of strength, the optimal concentration of acid sites and

metal sites, and the nature of their interaction remain unclear.

On the other hand, most of reported studies on hydroisomerization and

hydrogenation were performed in the vapor phase and a hydrogen pressure below 10

atm was used. A few researches carried out in the liquid phase using high pressure over

different catalysts revealed the great selectivity and conversion due to the limitation of

cracking activity at these reaction condition. Therefore, the aim of this dissertation was

to investigate to the influence of acidity provided by the replacement of Al and/or B

into SBA-15 framework on the catalytic and selectivity of the Pt/M-SBA-15 (where

M= M = Al-, B- and Al-B-) catalysts in the hydroisomerization and the hydrogenation

in the liquid phase and the hydrogen high pressure.

In electrochemical applications, chemically modified electrodes based on SBA-

15 derivatives presented an attracting trend due to the increase of mass transport, rapid

electron transfer, easy to develop and good analytical parameters. In the great number

of publications describing the PA detection, to the best of our knowledge, there is no

work reporting the use of the Pt/M-SBA-15 (where M = Al-, B- and Al-B-) materials

as electrocatalyst. Thus, in this dissertation, the Pt/M-SBA-15-GPE (where M = Al-, B-

and Al-B-) modified electrodes were prepared and used for the detection of PA, an

analgesic and antipyretic agent, extensively recommended for treating pain and fever.

CHAPTER 2. EXPERIMENTAL

2.1. Preparation of catalysts

2.1.1. Direct synthesis procedure of M-SBA-15 (where M=Al and/or B)

The direct synthesis procedure of M-SBA-15 (where M=Al and/or B) is shown

in Fig 2.1.

Pluronic (P123) dissolved in HCl

Aluminium precursor or/and boric acid Stirred for 1h

Tetraethyl orthosilicate (TEOS)

Hydrothermally crystallized at 90 oC for 48 h

Aged at RT for 15h then at 40 oC for 24h

Filtered and washed

Dried and calcined at 550 oC for 6h (1 oC/min)

Al-SBA-15 Al-B-SBA-15 B-SBA-15

Fig 2.1. Direct-synthesis of M-SBA-15 (M = Al and/or B)

In a typical synthesis batch, 3.5 grams of P123 were dissolved in 100 mL of 1.5

M HCl under vigorous stirring. Then, aluminum isopropoxide were added and the

solution was stirred for another hour. After that, 8.5 g of TEOS were gradually dropped

and the solution was maintained at room temperature for 15 hours, and then at 40 oC

for another 24 hours. The resulted suspension was transferred into an autoclave and

crystallized at 90 oC for 48 hours. The obtained solid product was filtered, washed with

double distilled water, dried (85 oC; 8h) and calcined at 550 oC for 6 hours (heating rate

of 1 oC min-1).

SBA-15 modified with B and/or Al by direct hydrothermal method with

Al/B/Si molar ratios of 1/0/10 – 0.5/0.5/10 and 0/1/10 were synthesized. The obtained

materials were characterized by XRD, TEM, BET, TPD-NH3…

2.1.2. Indirect synthesis of B/SBA-15

The B/SBA-15 support was prepared by impregnation method with Si:B ratio of

10:1. H3BO3 (0.217 g) dissolved in water (10ml) and was added to 1g support SBA-15.

The mixture was stirred for 48 h at 60 oC. The solid was separated by centrifugation

oC in 12 h with a heating rate of 1 oC/min.

and washed with distilled water. Then it was dried at 95 oC for 90 min, calcined at 350

2.1.3. Synthesis of Pt/M-SBA-15 (where M=Al-, B- and Al-B-) catalysts

Synthesis procedure of Pt loaded on modified supports is illustrated in Fig 2.2.

H2PtCl6 (with various loading ) dissolved in 10 ml H2O and then added to 1g of

support. The mixture was stirred at 60 oC in 48 hours. The solid was filtered by

centrifugation and washed with distilled water until free of chlorine (checked with

AgNO3 solution). It was dried at 95 oC for 90 mins, calcined at 350 oC in 12 hours with

a heating rate of 1oCmin-1 and reduced under a flow of hydrogen (30ml.min-1) at 450oC

for 6 hours [2].

2.2. Electrochemical procedure

2.2.1. Preparation of Pt/M-SBA-15-GPE electrodes

The unmodified graphite electrode (GPE) was prepared by mixing 40 mg of

graphite powder and 15 µl of paraffin oil by hand in 30 minutes using pastle and

mortar. The Pt/M-SBA-15-GPE (where M = Al-, B- and Al-B-) was prepared by

thoroughly mixing 20 mg of graphite powder and 20 mg Pt/M-SBA-15 powder with 15

µl of paraffin oil. The obtained paste was put into the cavity of a teflon holder, in the

bottom of which a piece of pyrolytic graphite was inserted in order to assure the

electric contact. The obtained electrode surface was smoothed using a weighing paper.

When necessary, a new electrode surface was obtained by removing 1-2 mm of the

outer paste layer, and adding freshly modified paste [99].

Supports

Al-SBA-15; Al-B-SBA-15; B-SBA-15

H2PtCl6 solution

Impregnation 60oC 48h

Centrifugation

Washing

Drying 95 oC, 90 mins

Calcining at 350 oC for 12 h (1 oC/min)

Reducing in H2 at 450 oC, 6 h Pt/Al-SBA-15 Pt/Al-B-SBA-15 Pt/B-SBA-15

Fig 2.2. Synthetic procedure of Pt supported on modified supports (Al-SBA-15; Al-B-

SBA-15; B-SBA-15) [2]

2.2.2. Preparation of supporting electrolyte and standard solution of paracetamol

Supporting electrolyte of 0.1 M phosphate buffer solutions (PBS) (pH=7) were

prepared by mixing equi-molar KH2PO4 and K2HPO4 in distilled water and adjusted

the pH using drops of HCl (0.1 M) and NaOH (0.1 M).

1000 ppm stock solution of PA was prepared in PBS (pH=7) prior to

experimental study. Working solutions of different concentrations of PA in PBS were

prepared from 1000 ppm stock solution through the dilution.

2.3. Catalyst characterization techniques

2.3.1. X-Ray Diffraction

X-ray powder diffraction (XRD) has been used to identify crystalline phases and

can provide information on unit cell dimensions. This technique is also used to study

periodically ordered structures at atomic scales [120]. The wavelengths of X-rays are in

the same order of magnitude as the distance between lattice planes in crystalline

materials. Diffraction effects are observed when the X-ray radiation passes through the

material with the geometrical variation wavelength, leading to the interaction of the

electron cloud of the atoms and the radiation. Most crystals have many sets of planes

through their atoms. Each plane has a spectific interplanar distance and will give rise to

a characteristic angle of diffracted x-rays.

Fig 2.3 shows a two dimensional drawing of a reflection within a crystal sample.

The lattice distance can be calculated using Bragg’s law.

n λ =2dhklsinθ (2.1)

where n is the order of diffraction, λ the wavelength, dhkl the distance between



Fig 2.3. Schematic illustration of diffraction according to Bragg’s law.

lattice planes and θ the angle of the incoming light.

For amorphous materials, such as mesoporous silica, there are no periodic

atomic planes but this technique is still useful for characterization of the ordered pore

structure. Mesoporous materials with periodically ordered pores give reflections for

low angles, 2θ < 3°.

In this thesis, powder X- ray diffraction patterns were recorded with a Brucker

D8 Advance diffractometer using CuKα radiation (λ=1.5405 Ao) at The Faculty of

Chemistry – HaNoi University of Science. Patterns were collected in steps of 0.02o

(2θ) over the angular ranges 0,5-8o (2θ).

2.3.2. Transmision electron microscopy (TEM)

TEM is a technique has been used to study the structure of solid materials. In

this method, electrons are scattered in a thin sample when a beam of electrons is

transmitted through. The transmitted electrons are focused on a fluorescent screen by

electromagnetic coils and the image is formed. The image contrast originates from

mass-thickness differences where thicker regions of the specimen absorb or scatter

more of the electrons compared to thinner regions [120].

TEM image presents the size distribution and shape of metal particles in

supported and unsupported catalysts to be characterized down to the level of atomic

resolution. It can also be used to study pore structures in the mesoporous silica.

Transmission electron microscopy (TEM) analyses were performed with a

JEM1010-JEOL microscope and an accelerating voltage of 100 kV in National

Institute of Hygiene and Epidemiology - Viet Nam.

2.3.3. Fourier Transformed Infrared Spectroscopy (FT-IR)

Fourier transformed infrared spectroscopy (FT-IR) is a technique used for

studying functional groups on the surface of materials [121]. The discrete energy

levels were employed for vibrations of atoms in these groups. Each groups of atoms in

the material can absorb light which is transmitted through the sample with a specific

energy. This occurs when the frequency of the incoming light corresponds to the

frequency of vibrations in bonds between atoms. The vibration energy depends on the

masses and chemical environment of the atoms, the type of vibration.

By scanning over a range of wavelengths and recording the amount of

transmitted light for each wavelength it is possible to determine which functional

groups that are present on the surface of the material.

A Fourier transform infrared spectrometer (FT-IR 6700 NRX Thermo-Nicolet

IR-Raman) in Laboratory of Petrochemical and Catalysis Adsorption Materials of

Hanoi University of Science and Technology was used to examine the functional

groups of the samples.

2.3.4. Temperature Programmed Desorption (NH3-TPD)

NH3-TPD method was used to determine the total acidity of materials [122].

The samples were heated to 150 oC (20 oC min-1) in 30ml high pure Helium flow.

Subsequently, the samples were cooled down to 30 oC in Helium flow. NH3 adsorption

was performed under ambient conditions and saturated for about 30 min in a flow of

10% ammonia in Helium (30 ml.min-1). Then, the samples were purged in a Helium

flow until a constant base line level was attained. Desorption of NH3 was carried out

with the linear heating rate (10 oC.min-1) in a flow of Helium from 30 oC to 600 oC.

The total acidity of the supports and fresh catalysts were evaluated by NH3-TPD

using a Altamira AMI902 apparatus in PetroVietNam Research and Development

center for Petroleum Processing (PVPro).

2.3.5. Nitrogen adsorption-desorption

Nitrogen adsorption-desorption is the most widely used technique to determine

the surface area and pore properties of porous materials. Based on the Langmuir theory

of monolayer physisorption, the Brunauer-Emmet-Teller (BET) theory extended to

multilayer adsorption.

The linear BET equation is showed in equation 2.3

(2.3)

Where n is the amount adsorbed gas at the relative pressure P/Po, nm is the

monolayer capacity, P is the measured pressure of the gas, Po is the saturated vapour

pressure of the gas at the temperature of adsorption, C is a constant.

The BET specific surface area (as) can be calculated from equation 2.4

(2.4)

In which  molecular cross-sectional area, m is the mass of adsorbent, NA =

6.023.1023 is the Avogadro constant.

Textural characteristics of catalysts were determined from the adsorption-

desorption isotherms of nitrogen at -196 oC using a Gemini VII 2390 V1.02

Micromeritics automated instrument at Hanoi National University of Education.

2.3.6. Thermal analysis

Thermal analysis measurements have been applied to characterize the thermal

stability. Thermogra vimetric analysis (TGA) and differential thermal analysis (DTA)

are two commonly used techniques for thermal analysis of solid materials. The TGA’s

principle based on the weight change of a sample is measured against time,

temperature or gas composition. TGA results are often presented as weight loss versus

either time or temperature [120].

The thermal analysis of the investigated catalysts was performed using a

Shimadzu DTG-60, DSC-60 analyzer at The Faculty of Chemistry – HaNoi University

of Science. The sample was analysed in air using the following temperature program:

20 min at room temperature, followed by a ramp of 10 o/min until 600 oC and kept for

5 min at this temperature.

2.3.7 Inductively coupled plasma optical emission spectrometry (ICP - OES)

ICP – OES is a method that can used to detect and measure weight percentage

of metal ions in samples. In this method, plasma energy is given to an analysis sample

to cause the collisional excitation. When the excited atoms return to low energy

position, emission rays (spectrum rays) are released and the emission rays that

correspond to the photon wavelength are measured. The element type is determined

based on the position of the photon rays, and the content of each element is determined

based on the rays' intensity.

The inductively coupled plasma optical emission spectrometry (ICP - OES) was

carried using an Agilent ICP – OES 715 at Universitat Politecnica de Valencia – Spain.

2.3.8. Pyridine-FTIR

Before the adsorption of the base, the powder samples were calcined at 450 oC

for 2 h under an air flow of 30ml/min. Self-supporting wafers obtained by

compression( 12 mg cm2) were outgassed in the IR cell at 400 oC at a residual

pressure of 1 atm. After the adsorption of the probe, the samples were purged for 2 h

with He at RT to remove the weakly sorbed species and then heated to each measuring

temperature.

Py-FTIR were recorded by using a Thermo Electron Nicolet 4700 FTIR

spectrometer with a resolution of 4 cm-1 at Universitat Politecnica de Valencia – Spain.

2.3.9. Energy Dispersive X-Ray Spectroscopy (EDS or EDX)

Energy Dispersive X-Ray Spectroscopy (EDS or EDX) is a chemical

microanalysis technique. This method is used in conjunction with scanning electron

microscopy (SEM) to characterize the elemental composition of the analyzed volume.

EDX analysis were recorded by using a JSM-5700 LV at Institute of Chemistry –

Vietnamese Academy of Science and Technology.

11B MAS NMR experiment was performed on a Brucker Advanve HD 400 MHz

2.3.10. 11B MAS NMR spectrocopy

spectrometer at Universitat Politecnica de Valencia – Spain. Sample was recorded with

a pulse < PI/12 with a recycle delay of 1s. A resonance frequency of 160.96 MHz, a

Brucker 4 mm MAS probe and the sample spinning rate of 10 kHz were applied.

BF3(OEt)2 was used as a reference.

2.4. Hydroisomerization activity test

For the hydroisomerization, the catalytic tests were performed in batch

experiments under stirring conditions by using a autoclave batch reactor from HEL

starting with 4 ml n-heptane and 10 mg catalyst (0.5% Pt/M-SBA-15 where M = Al-,

B- and Al-B-). The reactions were performed at different temperatures (200, 250 and

300 oC) under a performed of 30 at H2 and reaction times in the range of 3-24 h were

used. Before pressurization, the autoclave was flushed several times with H2. The

analysis of the gas and liquid products of n-heptane hydroisomerization were carried

out with a GC Varian STAR 3400 equipped with TCD and FID detectors using a factor

FOUR VF-1 MS column.

2.5. Hydrogenation activity test

The catalysts of 0.5% Pt/M-SBA-15 (0.097g) were tested in the hydrogenation

reaction of tetralin using 5 ml tetralin in a 316 – stainless steel autoclave batch reactor,

with hydrogen pressure of 15 – 25 at, reaction temperature was at 180 – 220 oC and the

stirring rate was at 150 r/min.

The products were filtered and analyzed by GC – MS using a 6890N/5975 Gas

Chromtograph – Mass Spectrometer instrument (Agilent Technologies, USA) equipped

with a fused – silica capillary column (HP-5MS) in Military Institute of Chemistry and

Environment, VietNam.

The experiments of hydroisomerization and hydrogenation were performed at

Department of Organic synthesis and Petrochemical Technology, School of Chemical

Engineering, Hanoi University of Science and Technology, VietNam and at

Department of Organic Chemistry, Biochemistry and Catalysis, University of

Fig 2.4. (a) The high pressure autoclave batch reactor and (b) schematic batch reaction system used for the n-heptane hydroisomerization and the tetralin hydrogenation

Bucharest, Romania.

2.6. Electrochemical measurements

All electrochemical measurements (cyclic voltammetry, electrochemical

impedance spectroscopy and square ware voltammetry) were performed using a PC

controlled electrochemical analyzer (AUTOLAB). A conventional three-electrodes cell

equipped with a Pt/M-SBA-15-GPE (where M = Al-, B- and Al-B-) modified carbon

paste electrode, as working electrode (geometrical area was 0.07 cm2), a Pt wire, as

counter electrode, and a Ag|AgCl,KClsat reference electrode was used.

Experimental conditions of cyclic voltammogramms: electrolyte, 0.1 M

phosphate buffer (pH 7); scan rate, 50 mV s-1; starting potential, -0.2, -0.5 or -0.75 V

vs. Ag/AgCl, KClsat.

The values of anodic and cathodic potential and intensities (Epa, Epc, Ipa, Ipc) are

estimated from the cyclic voltammograms.

The characteristic electrochemical parameters are obtained using the following

formulars:

(2.4) The peak to peak separation: Ep = Ep,c - Ep,a

The formal peak potential: Eo’= (Ep,a + Ep,c)/2 (2.5)

The peak current ratio: Ip,a/Ip,c (2.6)

The FWHM value is the full width at half maximum, estimated as the difference

between the two extreme potentials at which the intensity of current is equal to half of

its maximum value.

The peak current intensity is proportional with the scan rate, as describing by

the Randles-Sevcik equation 2.7:

Ip = 2.69 * 105 n3/2 A D1/2 ν1/2 Co (2.7)

where: Ip is intensity of current (in A), n is the number of electrons, A is the

active surface area (cm2), D is the diffusion coefficient (cm2/s), is the scan rate (in V/s)

and Co is the concentration in bulk solution (mol/cm3)

Where:

Ep,a, Ep,c: anodic and cathodic

potential, in V

Ip,a, Ip,c: anodic and catholic intensity,

in A

Fig 2.5. Cyclic voltammogram for a reversible system [95]

The quantitative analysis of PA was carried out by square wave voltammetry

using the Pt/Al-SBA-15-GPE modified electrode. Experimental conditions: electrolyte,

0.1 M phosphate buffer (pH 7); frequency, 25 Hz; amplitude, 10 mV; step potential,

0.75 mV; starting potential, -0.3 V vs. Ag/AgCl, KClsat.

The analytical parameters of working electrodes as sensibility, limit of detection

(LOD), linear range of concentration are obtained by square wave voltammograms. For

example, LOD is calculated for a signal-to-noise ratio of 3 using the formula: LOD =

3*SD/slope, where the slope and standard deviation (SD) correspond to the parameters

of the fitting calibration curve equation.

The EIS study was carried out at open circuit potential in the frequency range of

0.1 Hz to 104 Hz. The Nyquist plots recorded in the well known outer-sphere redox

probe of 1 mM K3[Fe(CN)]6/K4[Fe(CN)]6 in 0.1 M phosphate buffer (pH=7) at Pt/Al-

SBA-15-GPE modified electrode and GPE electrode, respectively.

The obtained experimental data were fitted based on an equivalent electric

circuit type either simple Randles [i.e, Rsol(CPEdl(RctW))] for GPE electrode, or a

modified Randles circuit [i.e., Rsol(CPEpore(Rpore(CPEdl(RctW))))] for Pt/Al-SBA-15-

GPE modified electrode, respectively. Both models circuit consisted from parallel and

serially connected resistors (Rsol, Rct Rpore), constant phase elements (CPEdl, CPEpore)

and Warburg impedance (W), respectively. The Rsol represents the resistance of the

electrolyte at the interface of the mesoporous catalyst recorded at high frequencies. The

CPEdl is the constant phase element corresponding to the double layer capacitance,

CPEpore is the constant phase element corresponding to the pore capacitance of Pt/Al-

SBA-15 matrix, Rct is the charge transfer resistance, Rpore is the intrinsic Pt/Al-SBA-15

material resistance and W is equivalent with the restricted diffusion of ions through the

multiple layers of non-homogenous distributed pores through the internal mesoporous

network of the composite material

Real sample analysis: The pharmaceuticals containing 500 mg PA per tablet

(“Paracetamol” from EuroPharm SA) were bought from local pharmacies and prepared

using the following procedure. Three tablets were weighed and then were carefully

ground with mortar to a fine powder. A quantity of homogeneous powders equivalent

to the average weight of one tablet was dissolved in 0.1 M phosphate buffer solution

(pH 7) by sonication for 10 min. The fresh prepared solution was analyzed applying

standard addition method and using the SWV investigation method.

All electrochemical experiments were done at Center of Electrochemistry and

Non-conventional Materials, Department of Chemical Engineering, Faculty of

Chemistry and Chemical Engineering, “Babes Bolyai” University from Cluj-Napoca

(Romania).

CHAPTER 3. RESULTS AND DISCUSSION

In chapter 3, the effect of preparation methods of modified support (section 3.1)

and characterizations of modified SBA-15 supports (section 3.2) are presented

respectively. The following section focuses on the characterizations of platinum

supported on modified SBA-15 catalysts (section 3.3) and their performance for hydro-

isomerization of n-heptane and hydrogenation of tetralin (section 3.4 &3.5). The last

part will present characterizations and application of these Pt catalysts in the detection

of paracetamol (section 3.6).

3.1. Effect of preparation methods of support.

Boron was introduced in the framework of SBA-15 by direct hydrothemal

synthesis (noted as B-SBA-15) and indirect method (noted as B/SBA-15) with Si:B

molar ratio of 10:1. The obtained materials were characterized by XRD, TEM, N2

u . a , I

B-SBA-15

B/SBA-15

SBA-15

0.5

adsorption-desorption, NH3-TPD, Py-FTIR.

Fig 3.1. Low angle XRD patterns of SBA-15, B/SBA-15 and B-SBA-15

(B)

(C)

(A)

Fig 3.2. TEM images of SBA-15 (A), B-SBA-15 (B) and B/SBA-15(C)

Low angle XRD patterns of pure SBA-15 and B-SBA-15 and B/SBA-15 are

given in Fig. 3.1. The XRD patterns presented three characteristic reflections of an

ordered SBA-15 mesoporous structure in the area 2Ɵ = 0.5-2o, which are assigned to

(100), (110) and (200) planes reflections respectively, indicating the mesoporous

structure of all samples.

In addition, the d100 spacing of B-SBA-15 (89.5 Ao) and B/SBA-15 (89.6Ao)

were a bit lower than that of pure SBA-15 (90.4 Ao). These results showed the ordering

of the SBA-15 framework was affected by boron incorporation, due to the smaller size

of boron compared to silicon which were also reported by Grieken [17].

Pore structure of pure SBA-15 and modified SBA-15 were also confirmed by

TEM images in Fig 3.2. All samples displayed a well-ordered hexagonal array, this is

in accordance with low angle XRD patterns.

The textual properties of SBA-15, B-SBA-15 and B/SBA-15 material were

determined by nitrogen physisorption isotherms and were illustrated in Fig 3.3.

All of samples showed the type IV isotherm of IUPAC classification, typical of

mesoporous materials. SBA-15, B-SBA-15 and B/SBA-15 samples have BET surface

area of 851 m2/g; 897 m2/g and 631 m2g, respectively. Textual properties of SBA-15,

) P T S g /

B-SBA-15 and B/SBA-15 material are summarized in Table 3.1.

m c ( d e b r o s b A y t i t n a u Q

Relative Pressure (p/po)

) g /

m c ( e m u l o V e r o P

(A)

l a t n e m e r c n I

(B)

Pore Width (Ao)

Fig 3.3. Nitrogen adsorption–desorption isotherm (A) and BJH pore size distribution

(B) of SBA-15, B-SBA-15 and B/SBA-15

Table. 3.1. Physicochemical properties of SBA-15, B-SBA-15 and B/SBA-15 samples

BET surface Pore Sample Pore size, Å area, m2/g volume, Å

SBA-15 851 42 0.76

B-SBA-15 897 60 1.21

B/SBA-15 631 44 0.68

BET surface area of B-SBA-15 sample is higher than that of pure SBA-15

material, the similar results had been reported by Grieken et al [17]. When boron was

incorporated into SBA-15 framework, it was at tetrahedral sites or trigonal sites [15].

The incorporation of boron into the framework changed the textual parameters of B-

SBA-15 sample. This result might be related with the shortening of the M-O bond

length due to the boron insertion into framework. In contrary, the impregnation method

decreased BET surface area and pore volume of B/SBA-15 sample. The reason was

that boron covered parts of porous material.

Ammonia temperature programmed desorption (NH3-TPD) profiles of SBA-15;

D C T %

B-SBA-15 and B/SBA-15 was shown in Fig.3.4.

Temperature, oC

Fig 3.4. NH3-TPD curves of SBA-15; B-SBA-15 and B/SBA-15

SBA-15 has no acidity because its NH3-TPD curve had no peak. NH3-TPD

profiles of modified SBA-15 samples (Fig. 3.4) obtained by direct synthesis and

indirect synthesis method present peaks in the range of 100 - 700 oC corresponding to

acid sites [123]. Therefore, the incorporation of boron in the mesoporous SBA-15

structure generated acidity of B-SBA-15 and B/SBA-15 material.

NH3-TPD of B/SBA-15 sample showed the desorption peaks at 200 oC and

<500 oC which related to weak and medium acid sites, whereas the NH3-TPD of B-

SBA-15 showed a broad desorption peak at temperature > 500 oC related to strong acid

sites [123]. The results of NH3-TPD analysis for SBA-15; B-SBA-15 and B/SBA-15

are given in Table 3.2.

Table. 3.2. Amonia TPD results of SBA-15; B-SBA-15 and B/SBA-15

Total acidity (NH3 μmol/g)

SBA-15 B-SBA-15 B/SBA-15

473 585 No acidity

Thus, the incorporation of boron into SBA-15 framework via two methods did

not affect the structure and morphology of SBA-15 but created the acid sites for the

modified SBA-15 materials. B-SBA-15 sample obtained by direct hydrothermal

synthesis has higher BET surface area and pore size compared to that of B/SBA-15

sample. All the textural characteristics of B-SBA-15 and B/SBA-15 material indicated

that the direct hydrothermal method had more advantages than the indirect method that

leads to higher surface area and well-ordered structure of the obtained material.

Therefore, the direct hydrothermal method has been used for synthesizing modified

supports in the next parts of this thesis.

3.2. Characterizations of modified SBA-15 supports

SBA-15 was modified by B and/or Al using direct hydrothermal method. The

modified supports, noted as Al-SBA-15; Al-B-SBA-15 and B-SBA-15, have the

Al/B/Si molar ratios of 1/0/10, 0.5/0.5/10 and 0/1/10, respectively. The obtained

materials were characterized by XRD, TEM, BET, NH3-TPD…

3.2.1. X-ray diffraction (XRD)

The low angle XRD patterns of modified SBA-15 by aluminum and/or boron

are presented in Figure 3.5.

Fig 3.5. Low angle XRD patterns of SBA-15; M-SBA-15 (M=Al and/or B) samples.

When the molar ratio of Al/B/Si changed, all samples showed intensity of

diffraction peaks corresponding to (100), (110) and (200) planes reflections

respectively in 2Ɵ range of 0.5-2o. The three peaks demonstrated that the synthesized

M-SBA-15 samples (where M = Al and/or B) had highly ordered mesoporous

structure. The intensity of characteristic diffraction peak (100) of modified SBA-15

samples changed little compared with that of pure SBA-15. The reason could be the

difference of cation radiuses of Al3+ (0.51 Å); B (0.23 Å) and Si4+ (0.42 Å) which

changed M-O distance in the SBA-15 framework [17] [124].

3.2.2. Nitrogen physisorption isotherms.

The textural properties of modified SBA-15 samples by Al and/or B, determined

by nitrogen physisorption isotherms, were illustrated in Fig 3.6.

(A)

Fig 3.6. Nitrogen adsorption isotherms and (A) Pore size distribution of SBA-15; Al-SBA-15, Al-B-SBA-15; B-SBA-15 (B).

(B)

Fig 3.6 showed the type IV isotherms as IUPAC classification with H1

hysteresis loop (Fig 3.6A), which is associated with porous materials consisting of

well-defined cylindrical channels [15]. All samples exhibit a steep jump at P/Po = 0.6-

0.75 due to capillary condensation in the cylindrical mesopores [17]. The textual

characteristics of investigated samples are presented in Table 3.3.

The modified SBA-15 samples obtained by direct synthesis method indicated an

increase in the pore size compared with the pure SBA-15 material. The similar results

have been reported by Grieken et al [17] and Ewaramoorthi [15]. When aluminum

and/or boron were incorporated into SBA-15 framework, aluminum remained at

tetrahedral centers or octahedral ones [17] and boron was at tetrahedral sites or trigonal

sites [15]. The presence of Al and B on the surface changed the textual parameters of

modified SBA-15 samples.

The surface area of modified supports which containing B increased with the

increase of B incorporation, these results are in agreement with the results of Grieken

Table 3.3. Textual characteristic of SBA-15 and the modified SBA-15 samples.

et al [17].

BJH BET surface BJH Desorption Desorption Sample area Pore volume Pore size (m2/g) (cm3/g) (Å)

Al-SBA-15 736.3 0.75 58 (Al:Si = 1: 10)

Al-B-SBA-15 879.9 1.19 60 (Al:B:Si=0.5:0.5:10)

B-SBA-15 896.8 1.21 60 (B:Si = 1:10)

3.2.3. Transition electron microscopy (TEM)

The structure and morphology of SBA-15, modified supports were analyzed by

transition electron microscopy. Fig 3.7 shows TEM images of SBA-15; Al-SBA-15;

Al-B-SBA-15 and B-SBA-15 samples.

As seen in Fig 3.7, the TEM images of the modified SBA-15 samples had

similar ordered mesoporous structure to pure SBA-15. This indicated that the

hexagonal mesostructure structure of modified SBA-15 were not destroyed after

modification. This result was consistent with the low angle XRD results and the

nitrogen physisorption isotherms.

(B) (A)

Fig 3.7. TEM images of SBA-15 (A); Al-SBA-15 (B); Al-B-SBA-15 (C) and B-SBA-15 (D)

(D) (C)

3.2.4. Fourier-transform infrared spectroscopy (FTIR)

FTIR method was used to identify the presence of functional groups in material

samples. Fig. 3.8 displays the FTIR spectra of modified SBA-15 samples.

All the samples exhibited peaks of almost the same frequency. The peaks

located around 1630 cm-1 are attributed to the hydroxyl bands of adsorbed water. The

broad peak at 3400 cm-1 is the O-H stretching vibration of Si-OH group on the

framework surface.

The structure vibrations of the molecular sieve were observed in the band of

1300-400 cm-1[ 65]. In the range of 1270-1050 cm-1, a shoulder at 1120 cm-1 attributed

to the asymmetric Si-O-Si stretching vibrations [65]. The T-O symmetric stretching

vibrations due to the intrinsic vibration of TO4 containing Al and Si are revealed by the

peak at about 800 cm-1[125]. The peak located at 470cm-1 corresponded to the bending

vibration of Si-O-Si. And the peak at 960 cm-1 is due to the presence of defects in the

pore channel which can be created by the isomorphous substitution of structural silicon

Fig 3.8. FTIR spectra of SBA-15 and modified SBA-15 samples

by other elements [65] .

3.2.5. EDX analysis

The EDX analysis was investigated for all modified SBA-15 samples. The

Table. 3. 4. Results of EDX analysis

results were presented in Figure 3.9 and Table 3.4.

Sample Al-SBA-15 Al-B-SBA-15 B-SBA-15

Element Weight, % Atomic, % Weight, % Atomic, % Weight, % Atomic, %

O 60.63 73.65 60.11 72.53 65.12 76.62

Al 8.45 5.99 1.83 1.31 --- ---

Si 29.91 20.36 38.05 26.15 34.88 23.38

The EDX analysis confirmed the presence of Si, Al, O elements on the surface

of the samples containing Al. For the samples of B-SBA-15 and Al-B-SBA-15, only Si

and O were observed from EDX analysis while boron, a light element, could not be

identified by the old model of EDX equipment [126].

(A)

(B)

(C)

Fig. 3.9. EDX spectras of Al-SBA-15 (A); Al-B-SBA-15 (B); B-SBA-15 (C)

3.2.6. 11B MAS-NMR spectroscopy

The 11B MAS-NMR spectrum of proton form of B-SBA-15 was shown in Fig

Chemical Shift (ppm)

Fig 3.10. 11B MAS-NMR for B-SBA-15 sample

3.10.

The spectrum of proton form of B-SBA-15 presented a broad signal at 40 ppm

to -40 ppm and the resonances are at -15 ppm and -35 ppm which could be contributed

by tetrahedral boron sites or trigonal boron sites [124]. Dongyuan et al [124] while

doping boron into ordered mesoporous materials (B-MCM-41) showed that 11B MAS-

NMR spectrum of as-synthesized samples has only one narrow band with a chemical

shift at -2.5 ppm which showed totally the incorporation of B in framework, whereas

the calcined samples display a broad 11B NMR band due to boron leaching out of

framework and the generation of species III or IV of other boron compounds.

3.2.7. Ammonia Temperature- Programmed Desorption (NH3-TPD)

NH3-TPD curves of modified SBA-15 samples (Al-SBA-15; Al-B-SBA-15 and

B-SBA-15) are shown in Fig 3.11.

NH3-TPD profiles of modified supports presented a broad desorption peak at

temperature >400 oC, a desorption peak at temperature of 250-400 oC and a peak at

100-250 oC corresponding to strong, medium and weak acid sites respectively [123].

As mentioned above, SBA-15 has no acidity. Therefore, the incorporation of aluminum

and/or boron in the mesoporous SBA-15 structure generated acidity in these materials.

Similar results were reported by Dragoi [14], Grieken[17] and Muthukumaran [127].

Fig 3.11. NH3-TPD curves of Al-SBA-15; Al-B-SBA-15; B-SBA-15 samples

Results of acidity measurement of Al-SBA-15; Al-B-SBA-15; B-SBA-15

Table 3.5. Acidic properties of Al-SBA-15; Al-B-SBA-15; B-SBA-15 samples according to NH3-TPD

samples are shown in Table. 3.5.

NH3 (µmol/g)

SBA-15 Al-SBA-15 Al-B-SBA-15 B-SBA-15

Total No acidity 728 726 473 acidity

8 100-250oC 7 15

50 250-400oC 60 52

670 >400oC 659 396

As can be seen from Table 3.5, the Al-SBA-15 sample presents a much stronger

acidity than B-SBA-15 sample due to a higher quantity of chemisorbed ammonia.

Similar observations of acidity for Al-SBA-15 and B-SBA-15 were also performed by

R.Van Griken [17]. It’s worth noticed that the only Al-containing material showed a

very similar acidity with SBA-15 material containing boron in a ratio of B:Al=0.5:0.5

thus suggesting a synergistic effect of the interaction of the two elements. Three

investigated supports presented the similar concentration of the weak and medium acid

sites while the strong acid sites showed a different distribution. The concentration of

strong acid sites on B-SBA-15 is much lower than that of the rest modified supports.

1610 1610 350oC 1450 1650 350oC 1450

) u

. a (

e c n a b r o s b A

300oC 300oC 1490

250oC 250oC

(B) (A)

1400 1600 1600

1400 Wavenumbers (cm-1) Wavenumbers (cm-1)

1450 1610

) u

. a (

350oC

e c n a b r o s b A

300oC

250oC

(C)

1600

Fig. 3.12. The Py-FTIR spectras of Al-SBA-15 (A), Al-B-SBA-15 (B), B-SBA-15 (C)

1400 Wavenumbers (cm-1)

3.2.8. FTIR spectra of chemisorbed pyridine

The pyridine adsorption IR spectra of modified supports were shown in Figure

3.12. The band at ~1450, 1490 and 1610 cm−1 could be seen in three samples. It is

reported that the band around 1450 and 1610 cm−1 are representative of the

coordination of pyridine with Lewis sites. The band at ~1490 cm−1 is attributed to both

the Brønsted acid and Lewis acid sites [22]. The band at ~1650 cm−1 only occured in

Py-FTIR spectra of Al-SBA-15 and it is assigned to the Bronsted sites.

Thus, the structure and morphology of mesoporous materials remained after the

incorporation of aluminum and/or boron into SBA-15 framework. Acid sites were

generated on the three supports. SBA-15 supports modified by B showed an increase of

surface area and the decrease of acidity. In the case of Al-B-SBA-15 sample, the

obtained acidity was similar to Al-SBA-15 sample due to a synergistic effect of the

interaction of B and Al.

3.3. Characterizations of Pt/modified SBA-15 catalysts

Three catalysts supported on modified SBA-15 materials with 0.5% platinum

loading have been prepared using the impregnation method. Characterizations of

investigated catalysts are presented base on the results from XRD, BET, TEM, NH3-

TPD.

3.3.1. Nitrogen physisorption isotherms

The textual properties of Pt/modified SBA-15 catalysts were determined by

nitrogen physisorption isotherms. The results are shown in Fig 3.13 and Table 3.6.

Nitrogen adsorption-desorption isotherm for all catalysts displayed typical type

IV isotherms with H1 hysteresis loop (Fig. 3.13), which is associated with porous

materials consisting of well-defined cylindrical channels [127]. All catalysts exhibited

a steep jump at P/Po=0.6-0.75 due to capillary condensation in the cylindrical

mesopores [17]. The pore size distribution of catalysts (Table 3.6) slightly shifted to

the smaller pore width compared with the corresponding supports. The incorporation of

Pt led to a decrease in BET surface area, total pore volume and pore size, suggesting

Fig. 3.13. Nitrogen adsorption-desorption isotherms and pore size distribution of catalysts.

Table. 3.6. Surface area and pore size of catalysts and the corresponding supports

that the deposition of platinum are partial blockage the support’s channels [61], 129].

Samples Samples SBET, m2/g Pore size, Å SBET, m2/g Pore size, Å

Al-SBA-15 736.3 0.5%Pt/Al-SBA-15 607 59 55

Al-B-SBA-15 879.9 0.5%Pt/Al-B-SBA-15 561.6 60 58

B-SBA-15 896.8 0.5%Pt/B-SBA-15 613.4 60 58

3.3.2. X-ray diffraction (XRD)

The low angle XRD patterns of Pt/modified SBA-15 catalysts is given in Fig

3.14.

The low angle XRD patterns of all samples exhibited three typical peaks of an

ordered SBA-15 mesoporous structure in the area 2Ɵ=0.5-5o range. The three peaks

were attributed to the (100), (110) and (200) planes reflections of hexagonal

mesostructure of three investigated catalysts. The further incorporation of Pt on the

modified SBA-15 supports do not affect their structure.

(C)

(B)

Fig 3.14. Low angle XRD patterns 0.5%Pt/Al-SBA-15 (A); 0.5%Pt/Al-B-SBA-15 (B) and 0.5%Pt/B-SBA-15 (C) catalysts

(A)

3.3.3. Transition electron microscopy (TEM)

The structure and morphology of catalyst samples were analyzed by transition

electron microscopy. As illustrated in Figure 3.15, three TEM images of catalysts

remained the well-ordered structure of SBA-15 material. This results are in well

accordance with low angle XRD patterns and the N2 physisorption isotherms. Pt

nanoparticles with diameter <5 nm over and inside the mesoporous structure can be

observed in TEM micrographs.

3.3.4. NH3-TPD profiles

The NH3-TPD profiles of catalysts contained 0.5%Pt are shown in Fig. 3.16.

NH3-TPD profiles of the investigated catalysts showed the medium acid sites

desorbed at 200 – 500 oC [22]. The total acidity of catalysts decreased compared with

the corresponding supports. This diminution of acidity of catalysts can be contributed

by the replacement proton H+ of silanol by Pt or coverage effect. So, the platinum

loading reduced the total acidity of catalysts.

(A) (B)

Fig. 3.15. TEM images of 0.5%Pt/Al-SBA-15; 0.5%Pt/Al-B-SBA-15 and 0.5%Pt/B-SBA-15 .

D C T %

(C)

Fig 3.16. NH3-TPD curves of 0.5% Pt/Al-SBA-15; 0.5% Pt/Al-B-SBA-15 and 0.5% Pt/B- SBA-15 catalyst.

Temperature, oC

The deposition of the platinum not only reduced the acidity, but also change the

distribution of the acid sites of three catalysts. NH3-TPD profiles of the catalysts

presented the medium acid sites whereas that of corresponding supports showed strong

acid sites. The strong acid sites are in term of the amount of hydroxyl groups [22].

Therefore, during the impregnation, calcination and reduction of catalyst, the strong

Table. 3.7. Results in NH3-TPD of catalysts

acid sites decreased.

NH3 (µmol/g)

Total Weak acid Medium acid Strong acid

sites sites sites

8 50 670 728 Al-SBA-15

7 60 659 726 Al-B-SBA-15

15 52 396 473 B-SBA-15

0.5%Pt/Al-SBA-15 81 295 160 536

0.5%Pt/B-Al-SBA-15 24 400 206 630

0.5%Pt/B-SBA-15 28 245 82 355

The highest acidity has been measured for Pt/Al-B-SBA-15 which also shown

the higher concentration of the strong acid sites. The Pt/B-SBA-15 catalyst presented

the lowest concentration of the strong acid sites which was 5 times lower than that of

the corresponding support. These results demonstrated that the anchoring of platinum

on these catalysts occurred via the direct interaction of H2PtCl6 with the very strong

acid sites of the support that is in a total agreement with the mechanism proposed by

Regalbuto et al [128]. Detail research of Regalbuto showed that during impregnation,

Pt complexes which arised from chloroplatinic acid (CPA) onto alumina existed at

-2 and PtCl5(OH)-2 in the lower

neutral valent PtCl4(H2O)2 in the mid pH range, PtCl6

-2 in high pH.. The long-term deposition of Pt over alumina

pH of 5, PtCl4(OH)2

depends on pH of CPA solution which changed during impregnation. The measured

decrease of the acidity exceeds that of the external surface, thus giving an indirect

evidence of the presence of Pt inside the pores.

3.4. Performance of platinum supported on modified SBA-15 catalysts for hydro-isomerization of n-heptane

The previous sections showed the effect of Al, B on the acidic properties of the

Pt/M-SBA-15 (where M = Al-, B- and Al-B-) catalysts. In this part, the investigated

bifunctional catalysts were used in hysdroisomerization of n-heptane to study the

catalytic behaviour.

3.4.1. Effect of the acidic supports on hydroisomerization activity of catalysts

The performance of catalysts with various supports including Al-SBA-15, Al-B-

SBA-15 and B-SBA-15 were carried out at the reaction condition of 250 oC, 30 at, 12

hours The content of platinum was maintained at 0.5% in all catalysts.

The GC/MS analysis of liquid products confirmed the presence of isomer

products containing methylhexanes and dimethylpentanes. These branched heptanes

were also reported by Ping Liu [61] and Takeshi Sugii [129] and agreement with the

mechanism proposed by Guisnet [36]. Diethylpentane and alkenes haven’t been

detected in the product mixtures.

Conversion of n-heptane over the investigated catalysts is illustrated in Table.

3.8 and Figure 3.17. The 0.5% Pt/M-SBA-15 (where M = Al-, B- and Al-B-) catalysts

showed the activity for hydroisomerization with the conversion of n-heptane at 38, 42

and 28%, respectively. The Pt/Al-B-SBA-15 catalyst showed a slightly higher

conversion than the Pt/Al-SBA-15 one. The conversion of Pt/B-SBA-15 catalyst was

lowest compared to the Pt/Al-B-SBA-15 and Pt/Al-SBA-15 catalysts. These results

showed that the activity of catalysts depend on the strong acid sites of supports which

have been responsible for the isomerization reaction[130]. As already reported in Table

3.7, the deposition of platinum on modified supports decreased the acidity, especially

the strong acid sites. The diminution of the strong acid sites on the Pt/Al-SBA-15

catalyst was larger than that of Pt/Al-B-SBA-15 catalyst. The activity of Pt/B-SBA-15

Table 3.8. Conversion of n-heptane over the Pt/M-SBA-15 (M=Al and/or B) catalysts.(The reaction condition of 250 oC, 30 at, 12 hours)

catalyst also paralleled its lowest acidity.

Samples Conversion, %

Pt/Al-SBA-15 31

Pt/Al-B-SBA-15 39

Fig 3.17. Conversion of n-heptane over the three catalysts of 0.5%Pt/Al-SBA-15; 0.5%Pt/Al- SBA-15 and 0.5%Pt/B-SBA-15.

Pt/B-SBA-15 20.2

The selectivity of branched isomers for all catalysts are shown in Figure 3.18.

Methylhexanes selectivity obtained at 82%, 78% and 93% for Pt/Al-SBA-15, Pt/Al-B-

SBA-15 and Pt/B-SBA-15 respectively while the maximum selectivity of

dimethylpentanes was at 22 % for Pt/Al-B-SBA-15. For Pt/Al-SBA-15 and Pt/B-SBA-

15, the dimethylpentanes selectivity was only at 18% and 7% respectively. It can be

seen that the selectivity of methylhexanes was much higher than that of

dimethylpentanes. The differences of branched isomers selectivity could be explained

in term of the acidity [38]. In the hydroisomerization process, the higher acid strength

the catalysts possess, the more favourable the branched products are formed. The

intermediate carbenium ions were kept relatively longer residence time on the acid

sites and the latter intermediates to be isomerized [38, 134, 135] . Thus, the obtained

selectivity of dimethylpentanes for Pt/Al-B-SBA-15 catalyst corresponding to its

The reaction condition of 250 oC, 30 at, 12 hours

Fig. 3.18. The selectivity of branched heptanes over the investigated catalysts

highest acidity compared to the acidity of the rest catalysts.

3.4.2. Effect of temperature and reaction time in the hydroisomerization of n-heptane

The hydrocracking reaction and coke formation always accompany the

hydroisomerization process. Thus, temperature and reaction time are the most

important factors in the hydroisomerization of long chain n-alkanes. In this work, the

hydroisomerization of n-heptane was investigated in the temperature range of 200 -

300 oC and the reaction time of 3 hours - 24 hours using the three catalysts of Pt/Al-

SBA-15, Pt/Al-B-SBA-15 and Pt/B-SBA-15. The conversion of n-heptane and the

selectivity of branched isomers were shown in Figure 3.19 and Figure 3.20.

Figure 3.19 showed the same trends of the variation of heptane conversion

versus reaction time and temperature were obtained over all investigated catalysts. At

the short reaction time and low temperature, the conversion of heptanes increased

quickly while the slight increase were obtained at the large reaction time and higher

0.5% Pt/Al-B-SBA-15

0.5% Pt/Al-SBA-15

0.5% Pt/B-SBA-15

Fig. 3.19. The heptane conversion versus reaction time and temperature over the Pt/M-SBA- 15 catalysts (M=Al and/or B)

temperature (12 hours - 24 hours and 250-350 oC).

The selectivity of iso-heptanes for all catalysts is shown in Figure 3.20. In the

investigated range of time and temperature, all the catalysts showed high selectivities

for the isomerization to methylhexane as the main products.

The selectivity of methylhexane slightly decreased with the increase of the

reaction time and temperature. In the contrary, the selectivity of dimethylpentane for

all catalysts increased and reached the maximum selectivity value of 28% for the

Pt/AlSBA-15 and Pt/Al-B-SBA-15 catalysts at the reaction condition of 300 oC after

24 hours. The lower selectivity of 10% was reached for Pt/B-SBA-15 catalyst. This

behaviour was in agreement with the hydroisomerization mechanism reported by

Guisnet [36]. The hydroisomerization proceeded through successive branching from

normal to mono- then to di-branched alkane. So, the contrary variations of selectivity

were obtained for the hydroisomerization to methylhexane and to dimethylpentane.

These behaviours are in line with the measured acidity of catalysts shown in Table 3.6.

No diethylpentane has been identified in the reaction mixtures in the conditions the

Methylhexanes Methylhexanes Methylhexanes Dimethylpentanes Dimethylpentanes Dimethylpentanes

Fig 3.20. The variation of the selectivity to branched heptanes versus reaction time and temperature over the investigated catalysts (Pt/Al-SBA-15 (a), Pt/Al-B-SBA-15 (b), Pt/B-SBA- 15 (c)

catalysts were investigated.

3.4.3. Cracked product yield and coke formation

In the hydroisomerization condition, the hydrocracking and coke formation also

took place on the acidic sites and affected the catalytic activity. Figure 3.21 presents

the yield of cracked products at the temperature of 300 oC after 12 hours for three

Fig 3.21. The yield of the cracked product over the investigated catalysts (300 oC, 12 h)

investigated catalysts.

It can be seen from Figure 3.21, the yield of cracking products for all catalysts

were small (<6 %) indicating their low activity for cracking reaction. The yield values

were obtained at 5.5 % and 5.8 % for the Pt/Al-SBA-15 and Pt/Al-B-SBA-15

respectively. The Pt/B-SBA-15 catalyst showed very low yield of 2 %.

At the reaction condition, coke formation also accompanied the

hydroisomerization process [133]. The results of thermogravimetry analysis

(TGA/DTA) are given in Fig 3.22. The TGA/DTA curves showed low weight losses.

The endothermic peaks in DTA curves indicated the weight losses at low temperature

(< 100 oC) which were corresponding to the desorption of physically adsorbed water.

The weight losses at higher temperatures demonstrated by exothermic peaks in DTA

curves corresponding to combustion of coke forms onto the surface of the used

catalysts. Guisnet [133] reported the adsorption and condensation on acid sites of

alkene intermediates caused by carbonaceous deposits and low- temperature coke is

nonaromatic.

Fig 3.22. DTA/TGA curves of the investigated catalysts after 24hours reaction time

The contents of coke determined from the TGA curves of the separated catalysts

Table. 3.9. Coke content determined from the thermogravimetry analysis of the investigated catalysts after a 24 hours reaction time

after 24 hours reaction time were shown in Table 3.9.

Catalysts Coke content, %

Pt/Al-SBA-15 4.8

Pt/Al-B-SBA-15 4.0

Pt/B-SBA-15 1.1

These values were around 5 % for Pt/Al-SBA-15, 4 % for Pt/Al-B-SBA-15 and

only 1 % for Pt/B-SBA-15 catalyst. The results of cracked yield and coke formation

were in agreement with the different acidity of catalysts. The catalysts containing

boron showed an increase of activity and the less content of coke.

In the investigated range of temperature (200-300 oC) and time (24 hours), the

M-SBA-15 (M= Al and/or B) supports exhibited no isomerization activity but only a

small cracking activity. The addition of platinum to these supports provided activity in

the hydroisomerization reaction even for a weak acid support as B-SBA-15. The Pt/Al-

B-SBA-15 catalyst with the ratio of Al:B = 0.5:0.5 showed a slightly higher conversion

than Pt/Al-SBA-15 one. So, the presence of both aluminum and boron led to a more

efficient catalyst. The Pt/B-SBA-15 catalyst showed the lowest conversion. All the

investigated catalysts showed high selectivity for the isomerization to methylhexanes.

Dimethylpentanes was also produced but in a different extent, depending on the acidity

of the support. Cracked products were also detected but the yields were smaller than 5

% after the reaction time of 24 hours.

3.5. Performance of platinum supported on modified SBA-15 catalysts for hydrogenation of tetralin

Together with the hydroisomerization process which produces branched alkanes

with high octane number, the hydrogenation of PAHs is also an important process in

modern petroleum refining to upgrade quality of heavy fuel and increase cetane

number of diesel. Both of these processes take place on bifunctional catalysts. Thus,

the Pt/M-SBA-15 (M = Al and/or B) catalysts are expected to be active catalysts for

the hydrogenation of tetralin.

3.5.1. The results of GC-MS analysis of hydrogenation of tetralin

The hydrogenation of tetralin was carried out over the Pt/M-SBA-15 (M = Al

and/or B) catalysts in the temperature range of 180 – 220 oC and hydrogen pressure of

15 – 25 atm. The reaction products obtained after 3 hours was analyzed by GC-MS.

The GC-MS analysis of product samples showed that the obtained products are

cis-, trans-decalin, 2-methyl tetrahydroindane and naphthalene. This result is

consistent with the results obtained by Sato et al [71], Ferraz [73] and Valles et al

[134]. Over bifunctional catalysts, the hydrogenation of tetralin takes place through a

complex reaction scheme. The aromatic ring of tetralin can be dehydrogenation to

naphthalene or hydrogenation to decalin. According to V. A. Valles et al [134],

naphthalene formation was found to be dependent on the concentration of tetralin and

the hydrogenation rate. Tetralin can also undergo naphthenic ring isomerization or

naphthenic ring opening followed by dealkylation and cracking reactions to form alkyl

indane and alkyl benzene compounds.

3.5.2. Effect of reaction temperature and pressure on catalytic activity

The effect of reaction temperature on the tetralin conversion over three

investigated catalysts is illustrated in Fig 3.23.

At the reaction condition of 200 oC and 20 atm, the maximum conversion of

tetralin is reached at 40.8 %; 31.4 %; 23.7 % over the catalyst of Pt/Al-SBA-15, Pt/Al-

B-SBA-15 and Pt/B-SBA-15 respectively. Research result of Veronica A. Valles [134]

for tetralin hydrogenation using Ir-Pt-SBA-15 catalyst also showed that after 3 hours of

reaction time, the maximum conversion was obtained in the temperature range of 200-

220 oC. At higher temperature and pressure, the tetralin conversion decreased.

The higher temperature favors the formation of by-products. The heavy products

adsorbed on the acid sites, condensed to form coke. Coke deposition are responsible to

the deactivation of catalysts [90].

Cis/trans-decalin ratio decreased slightly and close to 2.3 in temperature range

of 180 – 220 oC. This result can be explained by the strong competition for adsorption

sites in which the cis-to-trans isomerization was blocked by the adsorbed tetralin [90],

138].

Fig 3.23. Effect of reaction temperature on the conversion of tetralin over investigated catalysts((A): Pt/Al-SBA-15; (B): Pt/Al-B-SBA-15; (C): Pt/B-SBA-15). The reaction condition: liquid phase; reaction time: 3 hours

Effect of pressure on the tetralin conversion (Fig 3.24) showed that when

hydrogen pressure increased in the range of 15 - 25 atm, the conversion of tetralin

increased and reached a maximum of 23.7 % at 20 at then decreased. Increasing the

pressure from 20 atm to 25 atm led to the decreasing of cis/trans-decalin ratio from 2.3

to 2.1. Similar results were reported by [90], 139]. At high pressure, hydrogen can be

dissolved easily in liquid phase, but reactants and products couldn’t diffuse out of the

pores of the catalyst, therefore coke were formed and led to the deactivation of catalyst.

It is noted that cis-decalin could be isomerized to trans-decalin while this reaction is

irreversible.

3.5.3. Effect of the acidity of modified supports on catalytic activity.

The hydrogenation of tetralin was carried out over 0.5 %Pt catalysts supported

on SBA-15 modified by Al and/or B in the optimum condition of 200 oC and 20 at,

reaction time of 3 hours.

Results from table 3.10 and Fig 3.25 showed that the lowest tetralin conversion

of 23.7 % is reached over the Pt catalyst supported on SBA-15 modified by only B. As

mentioned before, Pt/B-SBA-15 catalyst has the lowest acidity compared with Pt/Al-

SBA-15 and Pt/Al-B-SBA-15 catalysts. The maximum tetralin conversion of 31.4 % is

obtained over Pt/Al-B- SBA-15 due to its higher acidity. Thus, the differences in

acidity as well as surface area and pore size of catalysts affects tetralin conversion and

selectivity of products.

Table 3.10. Tetralin conversion and selectivity of products

0.5%Pt/Al-SBA- 0.5%Pt/Al-B-SBA- 0.5%Pt/B-SBA- Catalysts 15 15 15

Tetralin conversion,% 30.2 31.4 23.7

Selectivity, %

Cis-decalin 46.35 51.75 41.82

Trans-decalin 21.07 22.5 20.4

Naphthalene 12.68 10.05 9.37

2-Methyltetrahydroindane 5.05 3.84 3.25

Fig 3.25. The conversion of tetralin and cis/trans ratio over the investigated catalysts

Cis/trans ratio 2.2 2.3 2.05

The above results are compatible with the results obtained in hydrogenation of

tetralin on a more conventional Pt/γ-Al2O3 catalyst reported by Chan et al. [136] who

observed the highest cis-/trans-decalin ratio of 2.7 in a tricklebed reactor at 553 K;

however, the reaction in that work took place under more severe conditions (in the

presence of compressed CO2 at a pressure of 6.2 MPa, and a mass ratio of CO2 to H2 of

0.25). Vallés et al. [90] studied hydrogenation of tetralin using Pt/SBA-15, the results

showed that tetralin conversion could reach up to 89 - 95 % at 200 - 220 °C and 1.5

MPa. This result is much higher than the data obtained in this dissertation; however,

the amount of catalyst was 6.8 times higher than in the present study (18 g/mol tetralin

compared to 2.64 g/mol tetralin).

3.5.4. Coke formation

The results of thermogravimetry analysis (TGA) are given in Fig 3.26 and Fig

3.27. The contents of coke determined from the thermogravimetry analysis of used

catalysts after 3 hours reaction time were 6.03 %, 2.76 % and 0.29 % for Pt/Al-SBA-

15, Pt/Al-B-SBA-15, Pt/B-SBA-15, respectively.

Fig 3.26A. TG curves of Pt/ B-SBA-15 (A) after reaction.

(A)

(B)

Fig 3.26B. TG curves of Pt/ Al-SBA-15 (B) and Pt/Al-B-SBA-15 (C) catalysts after reaction

(C)

At the reaction condition, coke formation is due to the adsorption and

condensation on acid sites of unsaturated compounds [133]. All TGA curves showed

low weight losses. The weight losses at low temperature (< 100 oC) correspond to

desorption of physically adsorbed water. The weight losses at higher temperatures are

due to combustion of coke forms onto the surface of the used catalysts. The results of

coke formation were agreement with the different acidity of catalysts. The catalysts

containing boron showed the less content of coke.

3.6. The mesoporous catalysts of Pt loaded on modified SBA-15 material for the paracetamol detection

The previous sections showed the efficient catalytic activity of the 0.5% Pt

supported on modified SBA-15 material for the hydroisomerization and the

hydrogenation. Motivated by these results, the investigated catalysts above were

expected to be active catalysts in electrochemical processes. However, the very low

peak currents of paracetamol (PA) were observed when the 0.5%Pt/M-SBA-15-GPE

(where M=Al and/or B) electrodes were employed. Thus, the Pt-based catalysts with

Fig 3.27. Square wave voltammograms of 10-5M PA at the 1%Pt/M-SBA-15-GPE (where M=Al and/or B) electrodes in 0.1M phosphate buffer (pH=7).

1% Pt were prepared and applied in the detection of PA.

Peak currents of paracetamol were obtained from square wave voltammograms

recorded at the 1%Pt/M-SBA-15-GPE (where M=Al and/or B) electrodes in the

presence of 10-5M PA. The results (Fig 3.27) showed the maximum peak current were

observed at 1% Pt/Al-SBA-15-GPE electrode. Therefore, this electrode was selected

for investigations of electrochemical behavior and analytical characterization.

3.6.1. Characterization of 1%Pt/Al-SBA-15 catalyst

Textural characteristics of the 1% Pt/Al-SBA-15 material was determined by

XRD patterns, BET results, TEM images and ICP.

The low-angle XRD patterns of 1%Pt/Al-SBA-15 catalyst (Fig. 3.28) showed an

intense main diffraction peak and two weak peaks, which are associated with (100),

(110), (200) planes reflections respectively, indicating their ordered hexagonal

Fig 3.28. Low angle XRD pattern of 1%Pt/Al-SBA-15 catalyst

mesoporous structure.

N2 adsorption–desorption isotherms of Pt/Al-SBA-15 catalyst (Fig. 3.29)

showed type IV isotherms with H1 hysteresis loop, which corresponds to mesoporous

materials consisting of well-defined cylindrical channels. Physico-chemical parameters

of Al-SBA-15 support and Pt/Al-SBA-15 catalyst were presented in Table 3.11. It can

be seen from table 3.11 that the BET surface area and pore size distribution decreased

after introduction of platinum to the Al-SBA-15 support. This implied that the pore

surface was loaded with Pt nanoparticles. Platinum content of 0.89 % was measured by

inductively coupled plasma (ICP) method for Pt/Al-SBA-15 catalyst.

Fig 3.29. Nitrogen adsorption-desorption isotherms at 77K (A) and pore size distribution (B) applying BJH method in the desorption branch of 1%Pt/Al-SBA-15 catalyst.

Table 3.11. Surface area and pore size of Al-SBA-15 support and 1%Pt/Al-SBA-15 catalyst

(B) (A)

Pore size, Pt content, Samples SBET, m2/g Å % (ICP)

Al-SBA-15 736.3 58 ---

1%Pt/Al-SBA-15 522.05 56 0.89

TEM images of Pt/Al-SBA-15 catalyst showed highly ordered hexagonal arrays

of the mesopores with uniform pore size (Fig. 3.30). This result is in accordance with

low angle XRD pattern and BET result. Small black dots appeared in TEM image with

particle size of 2 – 5 nm confirmed platinum particles on the surface of catalyst.

Fig 3.30. TEM image of 1% Pt/Al-SBA-15 catalyst.

The characterization of the 1% Pt/Al-SBA-15 catalyst determined by XRD,

TEM, BET, ICP showed that the hexagonal mesoporous structure of the investigated

catalysts was not affected. The introduction of platinum led to the formation of Pt

nanoparticles over and inside the mesoporous structure and decreased the surface area.

3.6.2. Electrochemical characterization of 1%Pt/Al-SBA-15-GPE electrode material

The electrochemical characterization of 1% Pt/Al-SBA-15-GPE electrode

material was studied using cyclic voltammetry. Fig. 3.31 showed the CV curves

recorded at the Pt/l-SBA-15-GPE electrode in the absence and in the presence of 7.10-6

M PA.

CV curves from Fig 3.31 showed a peaks pair due to the oxidation of PA which

are placed at following anodic/cathodic potentials (Epa/Epc): +0.425/+0.312 V for Pt/Al-

SBA-15-GPE and +0.5/+0.22 V for GPE, respectively. The similar behavior was

recorded in the same potential windows at MCPE-PtMWCNTs–TX100 (i.e.: Epa =

0.362 V and Epc = 0.311 V) [92].

The electrochemical parameters of the investigated electrode material were

summarized in Table 3.12.

Fig. 3.31. Cyclic voltammograms at Pt/Al-SBA-15-GPE in absence (dot line) and in presence of 7 x 10-5 M of PA (solid line). Inset: CV at unmodified GPE in presence of 7 M of PA.

Table 3.12. The electrochemical parameters of the 1%Pt/Al-SBA-15-GPE electrode material.

Electrode ΔE, V Eo’, V Ipa/Ipc FWHM, mV

GPE +0.28 +0.36 3.55 83

1%Pt/Al-SBA-15-GPE +0.113 +0.369 1.99 107

The diminution of the Ipa/Ipc ratio value at Pt/Al-SBA-15-GPE electrode,

suggesting that the presence of Pt nanoparticles of in the sensing matrix (Pt/Al-SBA-

15-GPE) improve the reversibility of the studied electron transfer reaction. The same

reason could justify the increase of peak currents of PA at Pt/Al-SBA-15-GPE

electrode matrix, comparing with the current recorded at unmodified GPE.

The full width at half of the peak maximum height (FWHM) is 107 mV and 83

mV for Pt/Al-SBA-15-GPE modified electrode and GPE unmodified electrode,

respectively. These values of FWHM which were different from theoretical FWHM

(90.6/n [mV]) have been attributed to electrostatic effects due to the presence of

adjacent charged species [137].

Effect of scan rate

The influence of the potential scan rate on the voltammograms of PA at

1%Pt/Al-SBA-15-GPE (Fig 3.32) showed a shift towards positive and negative

direction of the anodic and cathodic potential peak respectively when the scan rate

Fig 3.32. Cyclic voltamogramms of 7 x 10-5 M PA at 1%Pt/Al-SBA-15-GPE recorded at different scan rate. Inset influence of scan rate on anodic peak currents intensities at Pt/Al- SBA-15-GPE () and GPE () electrodes (A).

increased.

From Table 3.13, the log I - log v dependency for the oxidation/reduction peak

has a slope which is close to the theoretical value from the well-known Randles-Ševcik

equation (i.e., 0.5). This behaviour indicated a diffusion-controlled redox process of

PA occurring to the Pt/Al-SBA-15-GPE modified electrode [95][96].

The obtained results for the electrochemical parameters demonstrated the

obvious electrocatalytic properties of Pt/Al-SBA-15-GPE electrode for the PA redox

process. The obtained electrochemical activity were improved by Pt NPs free active

sites and mesoporous structure of catalyst distributed on the electrode surface and

requested for an enhanced electron transfer process.

Table 3.13. Slope of log I versus log v dependence.

Slope of log I - log v dependence Electrode type anodic R2/n

GPE 0.491 ± 0.011 0.9969/14

Pt/Al-SBA-15-GPE 0.418 ± 0.024 0.9823/13

3.6.3. Electrochemical impedance spectroscopy measurements at

1%Pt/Al-SBA-15-GPE electrode

The Nyquist plots recorded in a redox probe of 1 mM

K3[Fe(CN)]6/K4[Fe(CN)]6 at 1%Pt/Al-SBA-15-GPE and GPE electrodes,

respectively, are shown in Fig 3.33. The depressed semicircle observed at Pt/Al-SBA-

15-GPE interface is characteristic to porous materials [138], indicating low interfacial

electron transfer resistance and good conductivity. Contrarily, at GCE electrode

Figure 3.33. Nyquist plots recorded at 1%Pt/Al-SBA-15-GPE modified electrode () and GPE unmodified electrode () (inset) into a solution containing 1 mM K4[Fe(CN)6]/K3[Fe(CN)6] + 0.1 M phosphate buffer (pH 7).

a remarkable capacitive loop is present.

Both equivalent electric circuit (Rsol(CPEdl(RctW)) for GPE electrode and

Rsol(CPEpore(Rpore(CPEdl(RctW)))) for Pt/Al-SBA-15-GPE modified electrode) were

used for fitting the obtained experimental data. The EIS fitting parameters are given in

Table 3.14. EIS fitting parameters for Pt/Al-SBA-15-GPE modified electrodes.

Table 3.14.

EIS parameters

GPE

Pt/Al-SBA-15-GPE

13.36 ± 1.24

31.24 ±2.77

Rsol (Ω cm2)

-

142.6 10-5 ± 24.14

CPEpore (S sn/cm2)

-

0.496 n1

-

33.12 ± 6.61

Rpore (Ω cm2)

1.127 10-5 ±1.71

70.49 10-3 ±10.98

CPEdl(S sn/cm2)

0.905

1 n2

Rct (Ω)

3917 ± 0.76

273 ± 8

W (S s1/2 / cm2)

337.4 10-5 ± 6.98

529.6 ±10-5 + 34

chi2

0.629 10-3

0.964 10-3

± values are relative standard errors expressed as %.

As expected, at GPE the great Rct value indicates a hindering of the electron

transfer process, while a 10 times decrease of the Rct was obtained at Pt/Al-SBA-15-

GPE modified electrode pointing out an easy electron transfer occurring at electrode

interface. The reason might be due to the presence of Pt nanoparticles and/or of the

mesoporous structure of the Pt/Al-SBA-15 material.

3.6.4. Analytical characterization of 1%Pt/Al-SBA-15-GPE electrode material

Calibration curve

The quantitative analysis of PA was carried out using the Pt/Al-SBA-15-GPE

modified electrode by square wave voltammetry (Fig 3.34). The calibration curve

shows excellent linearity over a concentration range 10-6 –10-5 M PA.

The linear regression equations are:

I/A = (-8.36 10-7 ± 2.66 10-7) + (1.68 ± 0.04 ) [PA]/M (R = 0.9968, n = 11 points) and

I/A = (2.8 10-9 ± 3.07 10-9) + (29.9 10-3 ± 0.5 10-3) [PA]/M (R = 0.9986, n = 10 points)

at Pt/Al-SBA-15-GPE modified electrode and GPE, respectively.

Fig 3.34. Square wave voltamogramms for different concentration of PA at Pt/Al-SBA-15- GPE modified graphite paste electrode (A) and calibration curve of Pt/Al-SBA-15-GPE modified graphite paste electrode () and GPE () for PA (B).

(B) (A)

Compared with the unmodified GPE electrode, the sensitivity of the Pt/Al-SBA-

15-GPE modified electrode was increased approximatively 60 times. This could be due

to the presence of Pt nanoparticles and mesoporous structure of Pt/Al-SBA-15 catalyst

in the electrode matrix. The estimated detection limit (for a signal-to-noise ratio S/N =

3) were 0.85 M at Pt/Al-SBA-15-GPE modified electrode. The obtained value are

lower comparatively with some reported in the literature : 1.1 M at CPE-CNT-poly(3-

aminophenol) [101]; 1.39 M at PEDOT/SPE [139]; 6 M at graphene oxide-GCE

[140].

3.6.5. Interference study

To investigate the interference for the determination of PA, the oxidation peak

of 7 M PA was measured in the presence of different concentrations of the most

common interference compounds like: 1 mM or 2 mM ascorbic acid (AA) and 3 M or

5 M uric acid (UA). Square wave voltamogramms at the investigated modified

electrode were given in Fig 3.36.

AA

UA

PA

Fig 3.35. Square wave voltamogramms recorded at 1%Pt/Al-SBA-15-GPE modified

electrode in a presence of a mixture of 7 x 10-6 M paracetamol, 9 x 10-3 M ascorbic acid and 10-6 M uric acid.

The possible interference for the determination of PA was also studied, under

the same experimental conditions. Thus, the oxidation peak of 7 M PA was

individually measured in the presence of different concentrations of the most common

interferents like: 0.9 mM ascorbic acid and 1 M uric acid. As seen in Fig 3.36, there is

almost no influence on the detection of PA, because the peaks corresponding to the

interfering compounds appear completely separated from the oxidation peak of PA.

3.6.6. Real sample analysis

The Pt/Al-SBA-15-GPE modified electrode was used to estimate the PA

concentration in different commercial tablets, using the standard addition method,

appropriate when samples have complex matrices.

(A)

(B)

Fig 3.36. SWVs (A) and calibration curve (B) for detection of PA from tablets using 1%Pt/Al -SBA-15-GPE modified electrode.

Table 3.15. Determination of PA from pharmaceutical tablets using 1%Pt/Al-SBA-15-GPE modified electrode

Sample Added, µM Found, µM Recovery, % RSD, %

PA (500 mg/tablet) 5 4.95 ± 0.13 99.6 ± 2.61 2.63

SWV measurements were performed under similar experimental conditions as

for the electrode calibration against PA. The same analysis was performed using three

different Pt/Al-SBA-15-GPE electrodes and the obtained data were used to calculate

the average value of the PA concentration for the analyzed samples.

The results were found in very good agreement with those obtained by the

pharmaceutical tablets producer (Table 3.15). It was found that the recovery of PA was

in the range of 96.99 – 102.21 %. The relative standard deviation (RSD) was smaller

than 3%. The excellent average recoveries of formulation tablets samples suggest that

the Pt nanoparticles present in the electrode matrix (Pt/Al-SBA-15-GPE) is able to be

used for PA detection from pharmaceutical tablets.

CONCLUSIONS

1. The incorporation of Al and/or B into SBA-15 framework did not affect the

structure and morphology of SBA-15 mesoporous material but created acid sites on

their surfaces. The further loading of platinum on the modified supports caused a

decrease of the surface area, but the ordered hexagonal mesoporous structure of SBA-

15 material remained unchanged. The presence of both Al and B in a ratio of 0.5:0.5

created a highest acidity for Al-B-SBA-15 support and the corresponding catalyst of

Pt/Al-B-SBA-15. The acidic properties of modified supports played a crucial role in

the catalytic behaviour of the Pt/M-SBA-15 catalysts (where M = Al and/or B).

2. The studies of the hydroisomerization of n-heptane indicated that all of

investigated catalysts exhibited the good catalytic activity in the reaction condition of

temperature (200-300oC), range of reaction time (24 hours). The best conversion of n-

heptane was reached at 39% over the Pt/Al-B-SBA-15 catalyst at 300 oC, 30 at after

reaction time of 24 hours. These catalysts showed high selectivity for the isomerization

to methylhexanes. Dimethylpentanes was also produced but in a different extent,

depending on the acidity of the support. Yield of cracked products and coke formation

were smaller than 5 % after the reaction time of 24 hours.

3. At the condition of temperature (180-220 oC), hydrogen pressure (15-25 at),

reaction time of 3 hours, the three investigated catalysts were also employed

successfully in the hydrogenation of tetralin to cis- and trans-decalin. The maximum

tetralin conversion of 31.4 % and the cis/trans-decalin ratio of 2.3 are reached over the

Pt/Al-B-SBA-15 catalyst at 200 oC and 20 at.

4. The mesoporous 1%Pt/Al-SBA-15 catalyst was used to prepare the modified

electrode material. The electrochemical behavior of PA at 1%Pt/Al-SBA-15-GPE

modified electrode was investigated by CV, SWV and EIS.

The analytical parameters showed a linearity over concentration range of 10-6 M

– 10-5 M PA, sensibility of 1.68 A/M, detection limit of 0.85 µM, no interference. The

recovery of PA in real sample was in the range 96.99% - 102.21% corresponding to the

relative standard deviation was smaller than 3%. The obtained results showed the

electro-catalytic activity of 1%Pt/Al-SBA-15 material and its potential application for

PA detection in real samples

PUBLICATIONS OF THE DISSERTATION

1. Ngô Thị Thanh Hiền, Trần Văn Lâm, Phạm Trung Kiên, Nguyễn Thị Tâm, Nguyễn

Hồng Lê, Trần Thị Thúy Hiền, Nguyễn Thị Hà Hạnh, Nguyễn Anh Vũ, Phạm Thanh

Huyền (2017), “Nghiên cứu ảnh hưởng của boron tới đặc trưng xúc tác Pt/B-SBA-15

cho phản ứng hydro hóa tetralin”, Tạp chí dầu khí, số 9, 30-38

2. Ngo Thi Thanh Hien, Le Van Tuyen, Nguyen Van Tuan, Pham Thanh Huyen

(2018), “Direct hydrothermal synthesis and post-synthesis grafting of boron onto SBA-

15: influence of synthesis method on the support of Pt containing catalyst for the

hydrogenation of tetralin”, Vietnam Journal of Catalysis and Adsorption, 7-issue 3,

52-57.

3. Ngo Thi Thanh Hien, Pham Trung Kien, Nguyen Anh Vu, Pham Thanh Huyen

(2019), “Direct synthesis of Al-B-SBA-15 and its application for Pt bifunctional

catalyst in the hydrogenation of tetralin”, Catalysis In Industry, Vol 11, No 1, 59-64

(SCI).

4. C. Rizescu, B. Cojocaru, N.T. Thanh Hien, P.T.Huyen, V.I. Parvulescu (2019),

“Synergistic B-Al interaction in SBA-15 affording an enhanced activity for the hydro-

isomerization of heptane over Pt-B-Al-SBA-15 catalysts”, Microporous and

Mesoporous Materials, Vol 281, 142-147 (SCI).

5. Thi Thanh Hien Ngo, I. C. Fort, Thanh Huyen Pham, G. L. Turdean (2020),

“Paracetamol detection at a graphite paste modified electrode based on platinum

nanoparticles immobilized on Al-SBA-15 composite material”, Studia UBB Chemia,

LXV, 1, 27-38 (SCI)

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APPENDIX