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: Assoc Prof Dr Phạm Thanh Huyền 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: Ta Quang Buu Library - Ha Noi University of Science and Technology VietNam National Library INTRODUCTION 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 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 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 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/MSBA-15 catalysts in electrochemical detection of paracetamol using chemically modified electrodes 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 Literature review (31 page); Chapter Experimental (12 pages); Chapter Results and discussion (46 pages); Conclusions (2 pages); Publications of the thesis (1 page); References (17 pages) CONTENTS CHAPTER 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 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 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 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, 0.5 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 (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 %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 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 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 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 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 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: 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 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 x 10-5 M of PA (solid line) Inset: CV at unmodified GPE in presence of 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 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 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 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]; µM at graphene oxide-GCE [140] 3.6.5 Interference study To investigate the interference for the determination of PA, the oxidation peak of µM PA was measured in the presence of 22 different concentrations of the most common interference compounds like: mM or mM ascorbic acid (AA) and µM or 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 x 10-6 M paracetamol, 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 mg/tablet) from pharmaceutical tablets using Pt/AlFound, µM 4.95 ± 0.13 Recovery, % RSD, % 99.6 ± 2.61 2.63 CONCLUSIONS 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 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 % after the reaction time of 24 hours At the condition of temperature (180-220 oC), hydrogen pressure (15-25 at), reaction time of hours, the three investigated catalysts were also employed successfully in the hydrogenation of tetralin to cis- and trans-decalin The maximum tetralin conversion of 24 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 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 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 boron tới đặc trưng xúc tác Pt/BSBA-15 cho phản ứng hydro hóa tetralin”, Tạp chí dầu khí, số 9, 30-38 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 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) 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, 281, 142-147 (SCI) Thi Thanh Hien NGO, Ioana Carmen FORT, Thanh Huyen PHAM, Graziella Liana TURDEAN (2020), “Paracetamol detection at a modified electrode based on platinum nanoparticles immobilized on Al-SBA-15 composite material”, Studia UBB Chemia, LXV, 1, 27-38 (SCI) ... distribution (B) of SBA- 15, B -SBA- 15 and B /SBA- 15 %TCD Table 3.2 Amonia TPD results of SBA1 5; 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... 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... 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 15 81