Tổng hợp hệ xúc tác trên cơ sở pt SBA 15 biến tính với al vàhoặc b và khả năng ứng dụng của chúng trong phản ứng hydroisome hóa n heptane, hydro hóa tetralin và phát hiện paracetamol

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

i

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.

ii


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


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
iv


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 hydroisomerization 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 nheptane ------------------------------------------------------------------------------------ 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-SBA15-GPE electrode ------------------------------------------------------------------------ 88

v

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

vi


LIST OF ABBREVIATIONS

AA

Ascorbic acid

BET

Brunauer-Emmet-Teller

CE

Counter electrode

CMEs

Chemically modified electrodes

CN

Cetane Number

CV

Cyclic voltammetry

DTA

Differential thermal analysis

EIS

Electrochemical impedance spectroscopy

FCC

Fluid catalytic cracking

FT-IR

Fourier transformed infrared spectroscopy

FWHM

Full width at half maximum

GCE

Glassy carbon electrode

GPE

Graphite paste electrode

ICP

Inductively coupled plasma method

LCO

Light cycle oil

LOD

Limit of detection

MSA

Amorphous silica-alumina

NH3-TPD

Ammonia Temperature- Programmed Desorption

PA

Paracetamol

PAHs

Polynuclear aromatic hydrocarbons

PBS

Phosphate buffer solution

Py-FTIR

FTIR spectra of chemisorbed pyridine

RE

Reference electrode

SAPO-n

Silicoaluminophosphate
vii

SBA-15

SWV


TEM

Santa Barbara Amorphous No 15

TEOS

Square wave voltammetry

TGA

Transmision electron microscopy

TMOS

Tetraethyl orthosilicate

UA

Thermogra vimetric analysis

WE

Tetramethyl orthosilicate

XRD

Uric acid
Working electrode
X-ray diffraction

viii

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 transdecalin..................................................................................................................... 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; AlB-SBA-15; B-SBA-15)........................................................................................... 39
ix

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 BSBA-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
x


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-SBA15). 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

xi


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

xii


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

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

xiii


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
1


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
been studied over many catalysts such as MoO 3/ZrO2-SO42-, Pt/WO3-ZrO2/SBA-15, 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
2


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-SBA15 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.

3


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.

4


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 SBA15 (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 m 2/g) and thick pore wall (3-6nm) [3]. These
characters enhance SBA-15 thermal and hydrothermal stability compared with MCM-

5


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,…

6


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].
7


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 BSBA-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
8


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 SBA15 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].
- Hybrid mesoporous SBA-15 for inmobilization onto SBA-15 of enzyme
[28]
-

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

for photocatalytic oxidation of phenylsulfophtalein [29]; Cu/SBA-15 for oxidation of
styrene [30] and oxidation of LPG [31]; VO x/SBA-15 for oxidative dehydrogenation of
n-butane; WO3/ZrO2 supported on SBA-15 for n-heptane isomerization [32].

9

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

10