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Chinese Journal of Catalysis
2006, Vol. 27, No. 9
Online: 25 September 2006

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Synthesis of TS-1 with High Catalytic Performance Using Inorganic SiO2-TiO2 Precursor ZHANG Haijiao, LIU Yueming*, HE Mingyuan, WU Peng* 2006, 27 (9):  749-751.  Abstract ( 1970 )   [Full Text(HTML)] () PDF (242KB) ( 790 )   The inorganic SiO2-TiO2 precursor having Si-O-Ti bonds similar to those present in the titanium silicalite (TS-1) molecular sieve was prepared through spontaneous dispersion of Ti(SO4)2 on amorphous porous silica by thermal treatment. The precursor was used as the silica and titanium sources to synthesize TS-1 using tetrapropylammonium hydroxide as the template under hydrothermal crystallization conditions. Characterization by X-ray diffraction, Fourier transform infrared spectroscopy, and scanning electron microscopy indicated that the TS-1 sample with MFI structure was well crystallized and the Ti atoms were successfully incorporated into the framework. The catalytic activity of TS-1 for the hydroxylation of phenol with dilute hydrogen peroxide showed that the treatment temperature of the SiO2-TiO2 precursor obviously influenced the catalyst performance, and the proper treatment temperature was about 450 ℃.

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Photocatalysis-Membrane Coupling Reactor and Its Application CUI Peng*, ZHAO Xianzhi, ZHOU Minjie, WANG Longde 2006, 27 (9):  752-754.  Abstract ( 2057 )   [Full Text(HTML)] () PDF (207KB) ( 1339 )   A photocatalysis-ceramic membrane coupling reactor was designed and used for the photocatalytic degradation of methyl orange. The rejection rate of TiO2, the filtrate flux, and the degradation rate of methyl orange in this reactor under the condition of back flushing were investigated. The rejection rate of the TiO2 photocatalyst particles reaches 99.9%. Within one period of partial reflux, the average degradation rate of the methyl orange solution is 10%, which is higher than that obtained in a cylindrical reactor.

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Preparation and Characterization of Meso/Macroporous Composite Oxides Al2O3-SiO2 WU Junsheng, LI Xiaogang*, DU Wei, DONG Chaofang 2006, 27 (9):  755-761.  Abstract ( 2244 )   [Full Text(HTML)] () PDF (663KB) ( 1060 )   Bimodal porous alumina-silica composite oxides were prepared via the sol-gel method using nonionic surfactant C16EO10 as the structure-directing agent. Tetramethoxysilane and aluminum nitrate were used as the silicon and aluminum precursors, respectively. Scanning electron microscopy and N2 adsorption/desorption measurements indicated that the composite oxides possess interconnected macropores and texture mesopores. The micrometer-range interconnected macropores were obtained by freezing the transitional structure of spinodal phase separation in the sol-gel process. The evolution of nanometer-range mesopores in the gel skeletons can possibly be attributed to the supramolecular templating by the nonionic surfactant. Energy dispersive spectroscopy proved that a large part of initially added aluminium was incorporated in the gel network. The Hammett indicator method and infrared spectra showed that the alumina-silica composite oxides were mild strong solid acids, and the amount of acid with acid strength H0 of -5.6 to -3.0 was 0.35 mmol/g. Moreover, these oxides contained abundant Lewis acid sites and less Bronsted acid sites.

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Calculation of Chemical, Material, and Heat Equilibrium for Ethylbenzene Synthesis through Alkylation of Dilute Ethylene with Liquid Benzene via Catalytic Phase Exchange Method ZHAO Xuesong1,2,3, LIU Shenglin1*, CHEN Fucun1, LIU Weicheng1, WANG Qingxia1, XU Longya1* 2006, 27 (9):  762-766.  Abstract ( 2200 )   [Full Text(HTML)] () PDF (219KB) ( 1150 )   The chemical, material, and heat equilibrium of ethylbenzene synthesis through alkylation of dilute ethylene with benzene via catalysis and a gas phase-liquid phase exchange method was analyzed and calculated. The isothermal temperature increase is 175.6 ℃ under the conditions of 1 mol/h ethylene, 4 mol/h N2, 3 mol/h benzene, 185 ℃, and 2.0 MPa. The calculation values of temperature increase, ethylene conversion, and ethylbenzene selectivity are in agreement with the experimental results. In the upper section of the reactor, after the heat exchange of fresh benzene of 35 ℃ with the out gas mixture of 202.6 ℃ from the reaction section, the equilibrium temperature of the system is 185.9 ℃, which is 0.9 ℃ higher than the reaction temperature. However, in the bottom section of the reactor, when dilute ethylene of 35 ℃ mixes with the liquid products of 202.6 ℃, the equilibrium temperature is only 153.5 ℃. This is because dilute ethylene needs a lot of heat energy to make the products from the liquid phase to the gas phase. Only when the dilute ethylene temperature is increased to 523 ℃ or 91.5 kJ heat energy is added, the equilibrium temperature can reach 185 ℃.

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Effect of Partial Substitution of K and Cu in LaMnO3 on Simultaneously Catalytic Removal of NOx and Soot PENG Xiaosheng, LIN He, SHANGGUAN Wenfeng, HUANG Zhen* 2006, 27 (9):  767-771.  Abstract ( 1928 )   [Full Text(HTML)] () PDF (324KB) ( 963 )   La0.8K0.2MnO3 and La0.8K0.2CuxMn1-xO3 was prepared by partial substitution of K for La in LaMnO3 and further partial substitution of Cu for Mn, respectively. The catalytic properties of the two catalysts for simultaneous removal of NOx and soot were evaluated through the temperature-programmed reaction technique. X-ray photoelectron spectroscopy (XPS) was adopted to investigate the effect of partial substitution from the aspect of the catalyst composition. The X-ray diffraction results showed that the two kinds of substitution promoted the formation of perovskite. To maintain the electroneutrality, Mn2+ turned to Mn3+ and even some Mn4+ after the partial substitution of K for La, which greatly improved both the activity and the selectivity of the catalysts. The partial substitution of Cu for Mn further promoted the transition of Mn3+ to Mn4+, which deactivated the catalysts a little but improved the selectivity of the catalysts again owing to the synergistic effects of Cu2+ and Mn3+. The XPS results indicated that surface Mn3+ and Cu2+ were the effective ions for the simultaneously catalytic removal of NOx and soot.

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Application of Coprecipitated Nickel Catalyst to Steam Reforming of Higher Hydrocarbons in Membrane Reactor CHEN Yazhong1,2, XU Hengyong1*, WANG Yuzhong1, XIONG Guoxing2* 2006, 27 (9):  772-776.  Abstract ( 1856 )   [Full Text(HTML)] () PDF (316KB) ( 867 )   The Ni/La-Al2O3 catalyst prepared by a coprecipitation method was employed to hydrogen production from steam reforming of higher hydrocarbons in a palladium membrane reactor. The catalyst was characterized by low temperature N2 adsorption, H2 temperature-programmed reduction, H2-O2 chemisorption, and X-ray diffraction. The results showed that there was a strong interaction between NiO and the support. In the Pd membrane reactor, due to the selective removal of H2 by the membrane, the yield of H2 was increased significantly, while the formation of methane was suppressed in contrast with the results in the conventional fixed-bed reactor. Even under the near-practical application conditions, e.g., high GHSV and small flux of sweep gas, high yield of H2 and membrane separation efficiency were still obtained. Furthermore, no degradation of the membrane was observed even under working conditions of 823 K and steam-to-carbon feed ratio 2.7. This suggested that it was feasible to realize H2 production from steam reforming of higher hydrocarbons using only one reactor and one nickel-based reforming catalyst at reaction temperatures lower than 823 K.

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Structural Characterization of Highly Stable Ni/SBA-15 Catalyst and Its Catalytic Performance for Methane Reforming with CO2 ZHANG Meili, JI Shengfu*, HU Linhua, YIN Fengxiang, LI Chengyue*, LIU Hui 2006, 27 (9):  777-782.  Abstract ( 2060 )   [Full Text(HTML)] () PDF (445KB) ( 835 )   A series of Ni/SBA-15 catalysts with different Ni contents (2.5% to 20%) were prepared by an incipient wetness impregnation method. The catalytic properties of the catalysts for the methane reforming with carbon dioxide were tested with a continuous-flow fixed-bed quartz reactor. The structure of the catalysts was characterized using X-ray diffraction and N2 adsorption. The results indicated that Ni/SBA-15 catalysts had a higher conversion of CH4 and CO2 under the reaction conditions. The 12.5%Ni/SBA-15 catalyst showed highly stable activity at 800 ℃ for 600 h. However, after reaction of 710 h, the conversion of CH4 and CO2 decreased about 50% and 25%, respectively. Coking was the main reason for the deactivation of Ni/SBA-15 catalysts. At high reaction temperatures, the mesoporous structure of SBA-15 was not destroyed and the pore walls of SBA-15 could prevent the aggregation of the nickel species. Upon insertion of nickel into SBA-15, small pores were formed besides the mesopores of SBA-15. The mesoporous structure of SBA-15 was not affected by the nickel species, however, the pore diameter, pore volume, and BET surface area were decreased.

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Effect of Electric Field on the Photocatalytic Performance of Titania Nano-Membrane HUANG Jinqiu, TANG Chaoqun*, MA Xinguo, HU Lianfeng, XUE Xia, ZHOU Wenbin 2006, 27 (9):  783-786.  Abstract ( 1782 )   [Full Text(HTML)] () PDF (254KB) ( 974 )   A TiO2 nano-membrane photocatalyst was prepared by the sol-gel method using foam-nickel as the radical material. In an in-house constructed photocatalytic reaction equipment with an electric field, the photo-electro-catalytic degradation of methyl orange solution was studied by applying a definite anode bias voltage on the catalyst. The effects of bias polarity, anode bias voltage, and initial concentration of methyl orange were investigated, and the differences between the photo-electro-catalysis and photocatalysis as well as photolysis were compared. The degradation efficiency of methyl orange can be greatly increased by applying the electric field. According to the theories of semiconductor and quantum mechanics, the photo-electro-catalytic reaction mechanism was discussed.

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Performance of Ru-, Sn- and Co-Promoted Pt/C Catalysts for Electrocatalytic Oxidation of Methanol LIU Shibin, LIU Yong, SUN Yanping*, HAO Xiaogang, ZHANG Zhonglin 2006, 27 (9):  787-792.  Abstract ( 1864 )   [Full Text(HTML)] () PDF (379KB) ( 962 )   Carbon-supported Pt-M (M=Ru, Sn, and Co) catalyst samples were prepared by the colloidal method and characterized by X-ray diffraction and energy dispersive X-ray spectroscopy. The results indicated that the Pt-M alloy particles distributed homogeneously on the carbon, the particle size was 2-6 nm, and the proportion of the metal element in the alloy particles coincided with that in the precursor. Cyclic voltammetry was carried out to measure the catalyst activity in different alkaline concentration electrolytes.The onset potential and spike potential for electrocatalytic oxidation of methanol changed and the peak currents increased with the increase in the alkali concentration. The catalyst activity decreased in the order Pt50Ru50/C>Pt50Sn50/C>Pt75Co25/C. The activity of Pt/C was enhanced markedly after adding Ru, and the peak current of Pt50Ru50/C reached 634.7 mA/mg in the solution of 1.0 mol/L NaOH+1.0 mol/L CH3OH at 25 ℃.

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Synthesis of Nanometer Magnesia with High Surface Area by Solid-State Chemical Reaction GUAN Hongbo, WANG Pei, ZHAO Biying, ZHU Yuexiang*, XIE Youchang 2006, 27 (9):  793-798.  Abstract ( 1827 )   [Full Text(HTML)] () PDF (419KB) ( 1029 )   Nanometer MgO samples with high surface area, small crystal size, and mesoporous texture were synthesized by thermal decomposition of MgC2O4•2H2O, which was prepared by solid-state chemical reaction between H2C2O4•2H2O and Mg(CH3COO)2•4H2O. The existence of steam accelerated the sintering of MgO during the decomposition process and MgO with surface area as high as 412 m2/g was obtained through calcining the precursor in flowing dry nitrogen at 520 ℃ for 4 h. The samples were characterized by X-ray diffraction, N2 adsorption, transmission electron microscopy, thermogravimetry, and differential thermal analysis. The as-prepared MgO was composed of nanocrystals with a size of 4-5 nm and formed a wormhole-like porous structure. In addition, the MgO had good thermal stability, and its surface area was still 357 and 153 m2/g after calcination at 600 and 800 ℃ for 2 h, respectively. Compared with the MgO sample prepared by the precipitation method, MgO prepared by the solid-state chemical reaction has similar pore size distribution, surface area, and crystal size. The solid-state chemical method has the advantages of low cost, low pollution, and high yield; therefore it appears to be a promising method for the manufacture of nanometer MgO in industry.

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Resolution of (R,S)-(4-Hydroxy-3-methyl-2-(2-propenyl)-2-cyclopenten-1-one) Catalyzed by Lipase in Ionic Liquid WANG Yongze1, MEI Lehe1, 2, ZHONG Chunlong1, 3, YAO Shanjing1, ZHU Ziqiang1 2006, 27 (9):  799-804.  Abstract ( 2187 )   [Full Text(HTML)] () PDF (346KB) ( 1027 )   The resolution of (R,S)-4-hydroxy-3-methyl-2-(2-propenyl)-2-cyclopenten-1-one ((R,S)-HMPC) by lipase was studied using ionic liquids and vinyl acetate as the reaction medium, respectively. The effects of the reaction medium, water activity, temperature, pH value, and cosolvent on the resolution were studied. The results showed that the ionic liquid ［bmim］PF6 was suitable for the reaction, and the initial rate of lipase in ［bmim］PF6 was 18.48 μmol/(g•min), which was much higher than that in vinyl acetate (9.18 μmol/(g•min). The half life of lipase in the ionic liquid was 74.53 h, which was higher than that in vinyl acetate (64.29 h), but the conversion of (R,S)-HMPC in ionic liquids was lower than that in vinyl acetate. The addition of an acyl donor could improve the conversion of (R,S)-HMPC in ionic liquids. The optimum reaction conditions in ［bmim］PF6 were water activity of 0.17, 40 ℃, and pH=7 same as those in vinyl acetate. When the cosolvent was added into the reaction system, the conversion in ［bmim］PF6 decreased whereas increased in vinyl acetate, which might be due to the different properties of the reaction media.

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Preparation of Pseudoboehmite with Large Pore Volume and High Specific Surface Area from Sodium Aluminate Solution by Hydrothermal Precipitation Using SB Po CAI Weiquan* 2006, 27 (9):  805-809.  Abstract ( 2585 )   [Full Text(HTML)] () PDF (321KB) ( 839 )   Pseudoboehmite with large pore volume and high specific surface area was successfully prepared by hydrothermal precipitation of sodium aluminate solution using SB pseudoboehmite (from Condea, Germany) as the seed, combined with dispersing and washing the precipitate with ethanol. Effects of the composition of the sodium aluminate solution (concentration of Al2O3 and molar ratio of Na2O/Al2O3) and the precipitation time on the precipitation yield of Al2O3 and Na2O and physico-chemical properties of the precipitates such as pore volume, specific surface area, and Na content were studied. When the sodium aluminate solution with Al2O3 concentration of 100-140 g/L and Na2O/Al2O3 molar ratio of 1.30-1.45 was used, about 30% precipitation yield of Al2O3 was obtained at 125 ℃ with a low seed ratio of 1.0. The obtained pseudoboehmite has a large pore volume of 0.84 cm3/g, a high specific surface area of 213.6 m2/g, and a low Na2O content less than 0.3% after the third precipitation cycle, and some of its properties are even superior to that of the SB powder. This study provides an preparation route for high value pseudoboehmite from the low-cost sodium aluminate solution.

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Kinetics of Lipase-Catalyzed Safflower Oil Hydrolysis in Solvent-Free and Microemulsion Media GAN Zhengyan1,2, WUMANJIANG Eli2*, XIAMUXI Kamar2 2006, 27 (9):  810-814.  Abstract ( 1935 )   [Full Text(HTML)] () PDF (317KB) ( 900 )   The kinetics of safflower oil hydrolysis catalyzed by a lipase from Aspergillus niger was investigated in a solvent-free medium and an AOT/isooctane/phosphate buffer microemulsion medium. The activation energy of the reaction was calculated from the Arrhenius plot to be 32.205 and 7.391 kJ/mol in the solvent-free medium and the microemulsion medium, respectively. The denaturation of the lipase in microemulsion was faster than that in the solvent-free medium. The apparent Michaelis constant Km was 0.135 mol/L in the solvent-free medium and 0.101 mol/L in the microemulsion medium. The experiment indicated that the inhibition of alcohol towards the lipase was reversible and competitive in both the solvent-free medium and the microemulsion medium. In addition, the inhibition by substrate appeared in these two systems when the substrate concentration exceeded 0.819 mol/L. The micelle catalysis theory and ester bond hydrolysis mechanism were used to explain the difference of lipase-catalyzed oil hydrolysis in the solvent-free medium and the microemulsion medium.

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Silver Modification of TiO2 Thin Films and Their Photocatalytic Activity REN Xuechang, SHI Zaifeng, KONG Lingren 2006, 27 (9):  815-822.  Abstract ( 2272 )   [Full Text(HTML)] () PDF (528KB) ( 679 )   Silver-modified TiO2 thin films were prepared by the photodeposition method, and their optical characteristics, distribution and size of silver clusters on the surface, and surface states were analyzed by diffuse reflectance ultraviolet-visible spectroscopy, scanning electron microscopy, and X-ray photoelectron spectroscopy, respectively. The photocatalytic activity of the films was tested using phenol degradation as the model reaction under the irradiation with ultraviolet light of different wavelengths in the presence or absence of oxygen. The results showed that when the Ag loading exceeded 0.015?0 mg/cm2, a remarkable blue shift of the absorption band of the Ag-TiO2 thin films was observed. In addition, the minor absorption peak around 346 nm appeared and shifted toward the long wavelength with increasing Ag loading. Silver particles photodeposited on the surface of the films were nonuniform and existed mainly as Ag0 with a little Ag2O. The content of O2 adsorbed on the surface of Ag-TiO2 was increased remarkably in contrast to that of the pure TiO2 thin films. The photocatalytic activity of the Ag-TiO2 thin films was greatly affected by their light absorption character. When irradiation by a low pressure mercury lamp in the presence of oxygen, the Ag-TiO2 thin films reached the maximum activity at a Ag loading of 0.052?3 mg/cm2, and the first-order rate constant was 1.16 times that of the TiO2 thin films. These results indicated that Ag+preferably deposited on silver clusters with a large n value, and the photocatalytic activity of the Ag-TiO2 thin films was mainly affected by their light absorption character, the size of silver clusters, and the adsorption ability of silver clusters to O2.

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Preparation of High Performance Methane Combustion Catalyst and Its Application to Natural Gas Catalytic Combustion Fan-Boiler ZHANG Xiaoyu, LIU Zhimin, WEI Zhenling, DU Xiaochun, GONG Maochu, CHEN Yaoqiang* 2006, 27 (9):  823-826.  Abstract ( 2189 )   [Full Text(HTML)] () PDF (182KB) ( 1658 )   A Co3O4-Fe2O3-MnO2 monolithic catalyst supported on a mixture of yttria-stabilized zirconia (YSZ)-Al2O3 and La-modified CeO2-ZrO2 oxygen storage material was prepared. The catalyst activity for methane combustion was measured in a microreactor, and a domestic natural gas premixed catalytic combustion fan-boiler prototype was developed on the basis of this methane combustion catalyst system. The monolithic catalyst has high activity and good thermal stability, and the natural gas premixed catalytic fan-boiler has the advantages of high thermal efficiency and low CO and NOx emissions. Hence it is an energy saving and environmentally friendly product with high efficiency.

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Hyperpolarized 129Xe NMR and Its Applications in Characterization of Porous Catalytic Materials LIU Yong1,2, ZHANG Weiping1*, HAN Xiuwen1, BAO Xinhe1* 2006, 27 (9):  827-836.  Abstract ( 2142 )   [Full Text(HTML)] () PDF (676KB) ( 942 )   Large spin polarization can be produced in 129Xe nuclei by laser optical pumping and spin exchange. Hyperpolarized Xe nuclear magnetic resonance (NMR) can increase the measurement sensitivity by several orders of magnitude compared to the thermally polarized Xe NMR. It is a powerful tool for studying the pore structure of a material and the particle distribution inside the pores. This paper introduced the basic principles of hyperpolarized 129Xe NMR and reviewed its applications in the characterization of porous catalytic materials, especially with respect to the inorganic microporous and mesoporous materials. The prospect of this technique was also discussed.