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 tt tiếng anh

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

THE ABSTRACT OF CHEMICAL ENGINEERING
DOCTORAL DISSERTATION

Ha Noi – 2020


The dissertation was accomplished in
HaNoi University of Science and Technology

Adviors:
1. Assoc. Prof. Dr Phạm Thanh Huyền
2. Prof. Dr Graziella Liana Turdean

Reviewer No.1:
Reviewer No 2:
Reviewer No 3:

The dissertation was defended before the scientific
committee at HaNoi University of Science and Technology

On the……………………………………

The dissertation information can be found at following libraries:
1. Ta Quang Buu Library - Ha Noi University of Science and
Technology
2. VietNam National Library


1
INTRODUCTION
1. Motivation
SBA-15 (Santa Barbara Amorphous) material is the most
frequency studied due to its interesting properties, such as high
surface area, large pore size, thick wall and high thermal stability.
Since the ordered mesoporous material SBA-15 has been synthesized
in 1998, 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 of studies were the substituting 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 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. Beside to meet the
demand for high quality diesel fuels, the hydrogenation of
polynuclear aromatic hydrocarbon (PAHs) is also an important

process to produce good performance diesel fuel with low aromatic
content.
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. The previous researches showed that noble
metal (such as Pt, Pd) are the most used metal 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 catalytic conversion was not high simultaneously with
high selectivity to branched isomers. The Bronsted acid sites
increased cracked products and micropores limited the diffusion of


2
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 MoO3/ZrO2-SO42-, Pt/WO3-ZrO2/SBA15, Pt/γAl2O3, 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 earlier studies showed 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
thesis. 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 the connection to 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 nanoparticles have also been
widely employed as modifiers for organic molecules. The above
conservations showed platinum nanoparticles supported on modified
mesoporous material (Pt/M-SBA-15 where M = Al-, B- and Al-B-)
can be considered to be electrochemical catalysts to improve the
performance of sensoring processes. Therefore, in this thesis, the 1%
Pt/M-SBA-15 catalysts were synthesized and their applicability in
the electrochemical detection of paracetamol were studied.
1.
Aim and 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


3
applicability in n-heptane hydroisomerization, tetralin hydrogenation
and paracetamol detection
2.
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/MSBA-15 catalysts in electrochemical detection of paracetamol using
chemically modified electrodes.
3.
The new contributions 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-15GPE 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.
Structure of the thesis
The thesis book has 113 pages including Introduction (4 pages);
Chapter 1. Literature review (31 page); Chapter 2. Experimental (12
pages); Chapter 3. Results and discussion (46 pages); Conclusions (2
pages); Publications of the thesis (1 page); References (17 pages).
CONTENTS


4
CHAPTER 1. LITERATURE REVIEW
Overview of mesoporous material, ordered mesoporous silica
SBA-15; the modified SBA-15 and their applications. Overview of
catalysts used for hydroisomeriztion of n-alkane, hydrogenation of
polynuclear aromatic hydrocarbon and detection of paracetamol. The
observations showed the attractive structure properties of
mesoporous SBA-15 material and the acidity of modified SBA-15
can be exploited for the bifunctional catalysts based on Pt/SBA-15
modified with Al and B in n-heptane hydroisomerization, tetralin
hydrogenation and paracetamol detection.Therefore, in this thesis,
the Pt/M-SBA-15 catalysts were synthesized and their applicability
in n-heptane hydroisomerization, tetralin hydrogenation and
electrochemical detection of paracetamol were studied.
CHAPTER 2. EXPERIMENTAL
2.1. Preparation catalysts
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 indirect synthesis of B/SBA-15 sample was
prepared by an impregnation method.
The (0.5%; 1%) Pt/M-SBA-15 catalysts (where M = Al-, B- or
Al-B-) were prepared by an impregnation method.
2.2. Electrochemical procedure
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.
Supporting electrolyte of 0.1 M phosphate buffer solutions
(PBS) (pH=7) were prepared by mixing equi-molar KH2PO4 and
K2HPO4 in distilled water. 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. Catalytic activity
Examine the applicability of 0.5% Pt/M-SBA-15 catalysts (where
M = Al-, B- and Al-B-) in n-heptane hydroisomerization, tetralin


5

I, a.u

hydrogenation; Examine the applicability of 1% Pt/M-SBA-15
catalysts in paracetamol detection.
2.2. Research methods
Catalyst characterization techniques include X-ray diffraction

(XRD), transmission electron microscopy (TEM), Fourier
Transformed Infrared Spectroscopy (FT-IR), Temperature
Programmed Desorption (NH3-TPD), Nitrogen adsorption, Thermal
analysis, Inductively coupled plasma optical emission spectrometry
(ICP - OES), IR Pyridine.
For the hydroisomerization and hydrogenation, the catalytic tests
were performed in batch experiments under stirring conditions by
using a autoclave batch reactor from HEL. Before pressurization, the
autoclave was flushed several times with H2. The products were
analysed by GC-MS.
Cyclic voltammetry (CV), Square wave voltammetry (SWV),
Electrochemical Impedance Spectroscopy (EIS) were used for
electrochemical measurements
CHAPTER 3. RESULTS AND DISCUSSION
3.1. Effect of preparation methods of support
Boron was introduced in the framework of SBA-15 by direct
hydrothemal synthesis (B-SBA-15) and post-synthesis method
(B/SBA-15) with Si:B ratio of 10:1.
XRD
patterns
of
modified SBA-15 (Fig 3.1)
present three characteristic
reflections
of
SBA-15,
B-SBA-15
which are assigned to (100),
B/SBA-15
(110) and (200) planes

SBA-15
reflections
respectively,
2
3
5
0.5 1
4
indicating the mesoporous
Fig 3.1. Low angle XRD patterns of SBAstructure of all samples. Pore
15, B/SBA-15 and B-SBA-15
structure of pure SBA-15
and modified SBA-15 were also confirmed by TEM images in Fig
3.2.


6
(C)

(A)

(B)

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

All of samples showed the type IV isotherm of IUPAC
classification, typical of mesoporous materials (Fig 3.3).
Table. 3.1. Physicochemical of properties of SBA-15, B-SBA-15 and B/SBA-15
samples
BET surface

Pore volume,
Pore size, Ao
Sample
area, m2/g
Ao
SBA-15
851
42
0.76
1.21
B-SBA-15
897
60
B/SBA-15
631
44
0.68

(A)
Relative Pressure

Incremental Pore Volume (cm3/g)

Quantity Absorbed (cm3/g

The incorporation of boron in the mesoporous SBA-15 structure
generated acidity of B-SBA-15 and B/SBA-15 material. 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 due to the obtained higher surface area,
well-ordered structure. Therefore, the direct hydrothermal method
has used for synthesizing modified supports in the next parts of this
thesis.

(B)
Pore Width

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


7

%TCD

Table. 3.2. Amonia TPD results of SBA15; B-SBA-15 and B/SBA-15

Temperature, oC

Total acidity (NH3 μmol/g)
SBA-15
B-SBA-15
B/SBA-15
No acidity
473
585

Fig 3.4. NH3-TPD curves of SBA15; B-SBA-15 and B/SBA-15

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.
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.
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. Presence of
all the above peaks
indicated typical features
Fig 3.5. Low angle XRD patterns of SBAof an ordered SBA-15
15; M-SBA-15 (M=Al and/or B) samples.
mesoporous
structure.
The samples retained the characteristic patterns of hexagonal
mesostructure after the modification.


8

3.2.2. Nitrogen physisorption isotherms.

Fig 3.6 showed that 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.

(A)

(B)

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).
Table 3.3. Textual characteristic of the modified SBA-15 samples.
Sample
Al-SBA-15
Al-B-SBA-15
B-SBA-15

BET surface
area (m2/g)
736.3
879.9
896.8

BJH Desorption Pore
volume (cm3/g)
0.75
1.19
1.21

BJH Desorption

Pore size (Å)
58
60
60

3.2.3. Transition electron microscopy (TEM)
The TEM images (Fig 3.7) confirmed that the materials have
a well-ordered mesoporous channel arranged is hexagonal structure .
(A) (B)

(C)

(D)

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

3.2.4. Fourier-transform infrared spectroscopy (FTIR)
All the samples (Fig 3.8) exhibit peaks of almost the same
frequency. The peaks located around 1630 cm-1 are 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.


9
In the range of 1270-1050
cm-1, a shoulder at 1120
cm-1 attributed to the
asymmetric
Si-O-Si

stretching vibrations. The
T-O symmetric tretching
vibrations due to the
intrinsic vibration of TO4
containing Al and Si are
revealed by the peak at
Fig 3.8. FTIR spectra of modified SBAabout 800 cm-1. The peak
15 samples
located
at
470cm-1
corresponded
to
the
-1
bending vibration of Si-O-Si. And the peak at 960 cm is due to the
presence of defects in the pore channel.
3.2.5. EDX analysis
The EDX analysis confirmed the presence of Si, Al, O elements
on the surface of the samples containing Al. For the samples of BSBA-15 and Al-B-SBA-15, only Si and O were observed from EDX
analysis while boron was not identified. (Table 3.4)
Table. 3.4. Results of EDX analysis
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

3.2.6. 11B MAS-NMR spectroscopy
The 11B MAS-NMR spectrum of proton form of B-SBA-15 and
sample were shown in Fig 3.10.
The spectrum of
proton form of B-SBA15 sample presented a
broad singal at 40 ppm to
-40 ppm and the
resonances are at -15
ppm
and -35 ppm could
Chemical Shift (ppm)
Fig 3.10. 11B MAS-NMR for B-SBA-15


10
be contributed by tetrahedral boron sites or trigonal boron sites.
3.2.7. Ammonia Temperature- Programmed Desorption (NH3-TPD)

NH3-TPD profiles of
modified supports (Fig 3.11)
present a broad desorption

peak at temperature >500oC,
a
desorption
peak
at
temperature of 250-500oC
and a peak at 100-250oC
corresponding to strong,
Fig 3.11. NH3-TPD curves of Al-SBA-15;
medium and weak acid sites
Al-B-SBA-15; B-SBA-15 samples
respectively. Therefore, the
incorporation of aluminum
and/or boron in the mesoporous SBA-15 structure generated acidity
in these materials.
3.2.8. FTIR spectra of chemisorbed pyridine
The band at ~1450, 1490 and 1610 cm−1 could be seen in three
of samples. The band at ~1450 and 1610 cm−1 are representative of
Lewis sites. The band at ~1490 cm−1 is attributed to both the
Brønsted acid and Lewis acid sites. The band at ~1650 cm−1 only
occured in Py-FTIR spectra of Al-SBA-15, it is assigned to the
Bronsted sites.
1610
1450

o

300 C
o

250 C

1490

(A)
1400
1600
Wavenumbers (cm-1)

350oC

1610

1450

300oC
250oC

(B)
1400
1600
Wavenumbers (cm-1)

Absorbance (a.u)

1650

Absorbance (a.u)

Absorbance (a.u)

350oC

o

1610

1450

350 C
300oC
250oC

(C)
1600
1400
Wavenumbers (cm-1)

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

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.


11
3.3. Characterizations of 0.5% Pt/modified SBA-15 catalysts
3.3.1. Nitrogen physisorption isotherms
All catalysts display type IV isotherms as IUPAC classification
with H1 hysteresis loop (Fig. 3.11), which is associated with porous

materials consisting of well-defined cylindrical channels.

Fig. 3.13. Nitrogen adsorption-desorption isotherms and pore size distribution of
catalysts.
Table. 3.6. Surface area and pore width of catalysts and the corresponding supports

Samples

SBET,
m2/g

Pore
size, Å

Samples

SBET,
m2/g

Pore
size, Å

Al-SBA-15

736.3

59

607

55

Al-B-SBA15
B-SBA-15

879

60

561.6

58

896

60

0.5%Pt/Al-SBA15
0.5%Pt/Al-BSBA-15
0.5%Pt/B-SBA15

613.4

58

(C)
(B)

% TCD

3.3.2. X-ray diffraction (XRD)
The low angle XRD plot presents three typical peaks which are
assigned to (100), (110) and (200) planes reflections respectively,
indicating the ordered hexagonal mesostructure of three catalysts.

(A)

Fig 3.14. Low angle XRD patterns
0.5%Pt/Al-SBA-15 (A); 0.5%Pt/Al-B-SBA15 (B) and 0.5%Pt/B-SBA-15 (C) catalysts

Temperature, oC
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.


12

(A)

(C)

(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

3.3.3. Transition electron microscopy (TEM)
TEM images of catalysts (Fig 3.15) remained the well-ordered
structure of SBA-15 material.

3.3.4. NH3-TPD profiles
NH3-TPD profiles of the investigated catalysts (Fig 3.14)
showed the medium acid sites desorbed at 200 – 500oC. The
deposition of the platinum not only reduced the acidity but also
change the distribution of the acid sites of three catalysts.
Thus, the structure of ordered hexagonal mesoporous materials
remained unchanged after the further deposition of platinum on the
modified supports although there are the decreases of the surface
area and the distribution of the strength of the acidity and the total
acidity of the catalysts
Table. 3.7. Results in NH3-TPD of catalysts

Al-SBA-15
Al-B-SBA-15
B-SBA-15
0.5%Pt/Al-SBA-15
0.5%Pt/B-Al-SBA-15
0.5%Pt/B-SBA-15

Weak acid
sites
8
7
15
81
24
28

NH3 (µmol/g)
Medium acid

Strong acid
sites
sites
50
670
60
52
295
400
245

659
396
160
206
82

Total
728
726
473
536
630
355


13
3.4. Performance of platinum supported on modified SBA-15
catalysts for n-heptane hydroisomerization
3.4.1. Effect of the acidic supports on hydroisomerization activity of

catalysts: The catalysts with the platinum content of 0,5% showed
the activity for hydroisomerization with the conversion of n-heptane
at 38, 42 and 28%, respectively.
Table 3.8. Conversion of n-heptane over the Pt/M-SBA-1 catalysts
Samples
Pt/Al-SBA-15
Pt/Al-B-SBA-15

Conversion, %
31
39

Pt/B-SBA-15

20.2

The Pt/Al-B-SBA-15 catalyst showed a slightly higher
conversion than the Pt/Al-SBA-15 one. The conversion of Pt/BSBA-15 catalyst was lowest compared to the Pt/Al-B-SBA-15 and
Pt/Al-SBA-15 catalysts.

Fig 3.17. Conversion of n-heptane
over the investigated catalysts

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

Methylhexanes selectivity (Fig 3.17) 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. Thus, the obtained selectivity of

dimethylpentanes for Pt/Al-B-SBA-15 catalyst corresponding to its
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 hydroisomerization of n-heptane was investigated in the
temperature range of 200 - 300 oC and the reaction time of 3 h - 24 h


14

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

At the short reaction time and low temperature, the
conversion of heptanes increased quickly while slight increases were
obtained at the large reaction time and higher temperature (12 hours 24 hours and 250-350 oC).
In the investigated range of time and temperature, all the
catalysts showed high selectivities for the isomerization to
methylhexane as the main products (Fig 3.20).

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))

3.4.3. Cracked product yield and coke formation
The contents of coke determined from the TGA curves of the
separated catalysts after a 24 hours reaction time were shown in
Table 3.9. These values were nearby 5% for Pt/Al-SBA-15, 4% for
Pt/Al-B-SBA-15 and only 1% for Pt/B-SBA-15 catalyst.
Table. 3.9. Coke content determined from the thermogravimetry analysis of
the investigated catalysts after a 24 hours reaction time
Catalysts
Pt/Al-SBA-15
Pt/Al-B-SBA-15
Pt/B-SBA-15

Coke content, %
4.8
4.0
1.1


15
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
3.5.1. The results of GC-MS analysis of hydrogenation of tetralin
The GC-MS analysis of a product sample obtained after 3 hours
showed that the obtained products are cis-, trans-decalin, 2-methyl

tetrahydroindane and naphthalene.
3.5.2. Effect of reaction temperature and pressure on catalytic
activity
At the reaction condition of 200oC and 20 atm, the maximum
conversion of tetralin is reached over there catalysts. Cis/transdecalin ratio decreased slightly and close to 2.3 in temperature range
of 180 - 220oC.

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).

Effect of pressure on the tetralin conversion (Fig 3.23) 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 20at then decreased.
3.5.3. Effect of the acidity of modified supports on catalytic activity.
The lowest tetralin conversion of 23.7 % is reached over the
Pt catalyst supported on SBA-15 modified by only B. The maximum
tetralin conversion of 47 % is obtained over Pt/Al-B- SBA-15.


16

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

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

Table 3.10. Tetralin conversion and selectivity of products

Catalysts

0.5%Pt/Al- 0.5%Pt/Al-BSBA-15
SBA-15

0.5%Pt/BSBA-15

Tetralin conversion,%

30.2

31.4

23.7

Selectivity, %
Cis-decalin
Trans-decalin
Naphthalene
2-Methyltetrahydroindane
Cis/trans ratio

46.35
21.07
12.68
5.05
2.2

51.75
22.5
10.05
3.84
2.3

41.82
20.4
9.37
3.25
2.05

The differences in acidity as well as surface area and pore size of
catalysts affects conversion of tetralin and selectivity of products.
3.5.4. Coke formation
The contents of coke determined from the thermogravimetry
analysis (Fig 3.26) 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/BSBA-15, respectively.


17
3.6. The mesoporous catalysts of Pt supported on modified SBA15 material for the detection of paracetamol
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/MSBA-15-GPE (where M=Al and/or B) electrodes were employed.
Thus, the Pt-based catalysts with 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-15GPE (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/AlFig 3.27. Square wave voltammograms of
10-5M PA at the 1%Pt/M-SBA-15-GPE
SBA-15-GPE
electrode.
(where M=Al and/or B) electrodes in 0.1M
Therefore, this electrode
phosphate buffer (pH=7).
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.

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


18

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

(A)

(B)

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
SBET, m2/g
Pore size, Å
Pt content, % (ICP)
Samples
Al-SBA-15
1%Pt/Al-SBA-15

736.3

58

---

522.05

56

0.89

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 Pt/Al-SBA-15-GPE
electrode material


19
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].
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 µM of PA.

The
electrochemical
parameters of the investigated
electrode
material
were
summarized in Table 3.12.
Table 3.12. The electrochemical parameters of the Pt/Al-SBA-15-GPE
electrode material.
FWHM,
Ipa/Ipc
Electrode
ΔE, V
Eo’, V
mV
GPE
+0.28
+0.36
3.55
83
1%Pt/Al-SBA+0.113
+0.369
1.99
107
15-GPE

The influence of the potential scan rate on the voltammograms
of PA at 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 increased.

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-15GPE () and GPE () electrodes
(A).


20
Table 3.13. Slope of log I versus log v dependence.
Electrode type
GPE
Pt/Al-SBA-15-GPE

Slope of log I - log v dependence
anodic
R2/n
0.491 ± 0.011
0.9969/14
0.418 ± 0.024

0.9823/13

The obtained results for the electrochemical parameters
demonstrated the obvious electrocatalytic properties of Pt/Al-SBA15-GPE electrode for the PA redox process.
3.6.3. Electrochemical impedance spectroscopy measurements at
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 Pt/Al-SBA-15-GPE and GPE
electrodes, espectively, 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
a remarkable capacitive loop is present.
Figure 3.33. Nyquist plots recorded at
Pt/Al-SBA-15-GPE modified electrode (∆)
and GPE unmodified electrode (ο) (inset)
into a solution containing 1 mM
K4[Fe(CN)6]/K3[Fe(CN)6] + 0.1 M
phosphate buffer (pH 7).

Both equivalent electric circuit (Rsol(CPEdl(RctW)) for GPE
electrode and Rsol(CPEpore(Rpore(CPEdl(RctW)))) for Pt/Al-SBA15-GPE modified electrode) were used for fitting the obtained
experimental data. EIS fitting paremeters showed the great Rct value
which indicated 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.


21
3.6.4. Analytical characterization of Pt/Al-SBA-15-GPE electrode
material
The quantitative analysis of PA was carried out using the Pt/Al-SBA15-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.

(A)
(B)

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).

Compared with the unmodified GPE electrode, the sensitivity of
the Pt/Al-SBA-15-GPE modified electrode was increased
approximatively 60 times. The estimated detection limit were 0.85
µM at Pt/Al-SBA-15-GPE modified electrode. The obtained value
are lower comparatively with some reported in the literature : 1.1 µM
at CPE-CNT-poly(3-aminophenol) [101]; 1.39 µM at PEDOT/SPE
[139]; 6 µM at graphene oxide-GCE [140].
3.6.5. Interference study
To investigate the interference for the determination of PA, the
oxidation peak of 7 µM PA was measured in the presence of


22
different concentrations of the most common interference
compounds like: 1 mM or 2 mM ascorbic acid (AA) and 3 µM or 5
µM uric acid (UA). Square wave voltamogramms at the investigated
modified electrode were given in Fig 3.36
Fig 3.35. Square wave
voltamogramms recorded at
AA
Pt/Al-SBA-15-GPE modified
electrode in a presence of a

UA
PA
mixture of 7 x 10-6 M
paracetamol, 9 x 10-3 M
ascorbic acid and 10-6 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.
(B)
(A)

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

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 %.


23
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-SBA15-GPE) is able to be used for PA detection from pharmaceutical
tablets
Table 3.15. Determination of PA
SBA-15-GPE modified electrode
Sample
Added,
µM
PA
(500 5
mg/tablet)

from pharmaceutical tablets using Pt/AlFound,
µM
4.95
±
0.13

Recovery, %

RSD, %

99.6 ± 2.61

2.63

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 investigated catalysts.
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