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Chinese Journal of Catalysis
2006, Vol. 27, No. 3
Online: 25 March 2006

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Preparation of Nano-TiO2 by Ethanol-Thermal Method and Its Catalytic Performance for Synthesis of Dibutyl Carbonate by Transesterification FENG Xiuli1,2, WANG Qingying1, WANG Gongying1*, QIU Fali1 2006, 27 (3):  195-196.  Abstract ( 1904 )   [Full Text(HTML)] () PDF (144KB) ( 1040 )   The preparation of nano-TiO2 powder by the alcohol-thermal method at atmospheric pressure using ethanol as the solvent, H2TiO3 as the precursor, and KOH, NaOH or NH3·H2O as the mineralizer has been presented. XRD result showed that the structure of TiO2 is anatase, and with the increase of mineralizer alkalinity, the average diameter of TiO2 becomes smaller, and the crystallinity of TiO2 becomes higher. The diameter and the crystallinity of TiO2 affect the catalytic activity of TiO2 for the synthesis of dibutyl carbonate (DBC) from dimethyl carbonate (DMC) and butyl alcohol. The anatase TiO2 obtained from KOH exhibits high catalytic activity, giving 61.9% conversion of DMC, 100% selectivity for DBC, and 61.9% yield of DBC. The conversion of DMC, selectivity and yield of DBC remain almost unchanged through four reuses.

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Synthesis of α-Hydroxy Esters by Glyoxylate-Ene Reaction in Lewis Acid Chloroaluminate Ionic Liquids SHEN Zhenlu*, HE Xijun, MO Weimin, XIE Yi, HU Baoxiang, SUN Nan 2006, 27 (3):  197-199.  Abstract ( 1989 )   [Full Text(HTML)] () PDF (176KB) ( 776 )   The chloroaluminate ionic liquid, composed of AlCl3 and 1-butyl-3-methylimidazolium chloride (［bmim］Cl), is used as the solvent and catalyst to synthesize α-hydroxy esters from alkene and glyoxylate via the glyoxylate-ene reaction. Under the reaction conditions of 15 ℃, 4 h, and AlCl3/［bmim］Cl molar ratio of 2, the ethyl α-hydroxy-4-phenyl-4-pentenoate with high yield (95.2%) is obtained in the reaction of α-methyl styrene and ethyl glyoxylate. Other α-hydroxy esters can also be obtained in high yields through the glyoxylate-ene reaction. Moreover, the chloroaluminate ionic liquid can be reused several times.

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An Adsorption Manometry Apparatus for High Resolution and Low Pressure Adsorption Isotherms LI Wenjun, WANG Yao, WANG Dezheng, WEI Fei 2006, 27 (3):  200-202.  Abstract ( 1764 )   [Full Text(HTML)] () PDF (242KB) ( 757 )

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Effect of Nd3+ Doping on Photocatalytic Activity of TiO2 Nanoparticles for Water Decomposition to Hydrogen HUANG Cuiying1, YOU Wansheng1,2*, DANG Liqin1, LEI Zhibin1,2, SUN Zhengang1, ZHANG Lancui1 2006, 27 (3):  203-209.  Abstract ( 2129 )   [Full Text(HTML)] () PDF (536KB) ( 785 )   The undoped TiO2 and Nd3+-doped TiO2 samples were prepared by sol-gel method and characterized by XRD, UV-Vis, TEM and N2 adsorption. The correlation between the photocatalytic activity for hydrogen evolution and the phase composition, BET surface area and intensity of light-absorption in UV region was investigated. For the undoped TiO2 samples, the particle size and agglomeration increased while its BET surface area and the intensity of light-absorption in UV region decreased with the increasing calcination temperature; the anatase to rutile phase transformation started at 600 ℃ and completed at 800 ℃; the photocatalytic activity of undoped TiO2 decreased with the increasing calcination temperature, and the sample calcined at 600 ℃ was the best because of the coexistence of a certain proportion of rutile/anatase mixed phase. For the Nd3+/TiO2 samples, Nd3+ doping inhibited the crystal phase transformation and the rutile phase began to appear at 800 ℃; moreover, Nd3+ doping restrained the growth of grain size, improved the dispersivity of the particles, and raised BET surface area. The more the doping amount was, the larger the BET surface area was. As the calcination temperature increases, the decreasing extent of the light-absorption intensity of Nd3+/TiO2 in UV region was lower than that of undoped TiO2. Nd3+ raised the photocatalytic activity for hydrogen generation and the optimum amount of Nd3+ doping was 0.1%, at which the photocatalytic activity of Nd3+/TiO2 was 3.5 times higher than that of undoped TiO2.

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Preparation of Copper-Based Catalysts for Methanol Synthesis by Acid-Alkali-Based Alternate Precipitation Method CEN Yaqing, LI Xiaonian, LIU Huazhang* 2006, 27 (3):  210-216.  Abstract ( 1704 )   [Full Text(HTML)] () PDF (608KB) ( 1128 )   A new copper-based catalyst for methanol synthesis was prepared by acid-alkali-based alternate precipitation (AP) method. The catalyst activity is the highest when the pH value of the mother solution alters in the range of 5.0 and 9.5 for three times. Compared with the catalysts prepared by other methods, the activity and thermal stability of the catalyst prepared by the AP method is the best. About 88% activity of the catalyst is remained after the thermal test, which is 8%～20% higher than that of other catalysts. Furthermore, the activity of this catalyst after the thermal test is higher than that of other catalysts before the thermal test. The catalysts were characterized by X-ray diffraction (XRD), N2 adsorption, differential thermogravimetric analysis (DTG), and scanning electron microscopy (SEM). XRD patterns show that the characteristic peaks of CuO and ZnO are far more broadened for the catalyst prepared by the AP method. From SEM photographs it is found that the grains of the catalyst prepared by the AP method are smaller, and the distribution of the grains is symmetrical. The crystal size of this catalyst is small. DTG patterns show that this catalyst requires the lowest reduction temperature. The primary reason for the high activity and thermal stability of the catalyst prepared by the AP method is that an amorphous sosoloid of CuO and ZnO is formed, which can increase the dispersion of the active components and the BET surface area of the catalyst.

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Interaction between Pd and ZnO during Reduction of Pd/ZnOCatalyst for Steam Reforming of Methanol to Hydrogen WANG Yanhua1, ZHANG Jingchang1, XU Hengyong2* 2006, 27 (3):  217-222.  Abstract ( 1837 )   [Full Text(HTML)] () PDF (367KB) ( 897 )   The changes in catalyst structure and species and charge transfer during the reduction of a co-precipitated Pd/ZnO catalyst with 15.9%Pd were investigated by temperature-programmed reduction, temperature-programmed desorption, temperature-programmed electronic conductivity, and X-ray diffraction. The effect of reduction temperature of the catalyst on the catalytic performance in steam reforming of methanol was also tested. The results showed that metallic Pd highly dispersed on ZnO over Pd/ZnO. The strong interaction between Pd and ZnO during the catalyst reduction with hydrogen led to hydrogen spillover from Pd to ZnO, which caused the reduction of ZnO near the metallic Pd and the formation of PdZn alloy. The reduction process proceeded as follows: PdO/ZnO → Pd/ZnO → PdZnO1-x/ZnO → amorphous PdZn alloy/ZnO → crystalline PdZn alloy/ZnO. Metallic Pd was present in a finely dispersed and amorphous-like state in Pd/ZnO prepared by co-precipitation, and because of that PdZn alloy could be formed at lower temperature than reported in the literature. When catalysts were reduced in the temperature range from 523 K to 573 K, PdZn alloy with size of 5～14 nm was obtained. At this moment, methanol conversion and CO2 selectivity reached maxima.

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A Periodical Density Functional Theory Study of Benzene Adsorption on Ag(100) Surface CAO Meijuan1, CHEN Wenkai1*, LIU Shuhong1, LU Chunhai2, XU Ying1, LI Junqian1 2006, 27 (3):  223-227.  Abstract ( 1804 )   [Full Text(HTML)] () PDF (4711KB) ( 1007 )   The adsorption of benzene on Ag(100) surface was studied by use of the density functional theory and periodical slab model. The adsorption energy and the geometric parameters on different adsorption sites showed that the hollow site was the most favorable adsorption site, followed by the bridge one, and the top site was the least stable mode. The adsorbed benzene molecule was parallel to the Ag(100) surface, and the benzene ring was distorted. The C-C bond was elongated in comparison with the free benzene molecule while the variation of C-H bond length was small. The C-H bonds of benzene bent away from the benzene-ring and Ag(100) surface. The calculation results showed that the interaction between the substrate and benzene molecule was relatively strong chemisorption. The detailed orbital and the charge population analysis was given, and the calculated results were compared with the experimental and theoretical results.

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Acidity and Catalytic Performance of BEA/MOR Intergrowth Zeolites QI Xiaolan1,2*, LI Bin1, LI Shijie1, LIU Xiyao1, LIN Bingxiong1 2006, 27 (3):  228-232.  Abstract ( 2214 )   [Full Text(HTML)] () PDF (310KB) ( 855 )   The acid properties of BEA/MOR (intergrowth of zeolite β and mordenite) samples with SiO2/Al2O3 molar ratio of 25 were characterized by temperature-programmed desorption of NH3 (NH3-TPD). There is a volcano-type relationship between the higher NH3-TPD peak temperature and the mordenite content of the BEA/MOR samples, and the NH3-TPD peak temperature reached the maximum at mordenite content of about 65%. In contrast, there is a linear relationship between the higher NH3-TPD peak temperature and the mordenite content of the mechanical mixtures of zeolite β and mordenite. No obvious difference in the acid strength existed between the BEA/MOR samples and the mechanical mixtures when the mordenite content was less than 50%. However, when the mordenite content exceeded 50%, the BEA/MOR samples possessed much higher acid strength than the mechanical mixtures. The BEA/MOR sample with 65% mordenite showed the highest acid strength, which was higher than that of the mordenite. The catalytic activity measurements of all the samples for methanol dehydration were carried out in a fixed-bed reactor under atmospheric pressure, temperature of 180 ℃, and methanol space velocity of 2 h-1. Dimethyl ether and water were the only products for each catalyst. No coke formation and catalyst deactivation were observed in the reaction of 6 h. There is a linear relationship between the methanol conversion and the mordenite content of the mechanical mixtures. The BEA/MOR samples with mordenite content higher than 40% showed higher catalytic activity than HM, and the BEA/MOR with 65% mordenite showed the highest methanol conversion. The catalytic activity of BEA/MOR also exhibited a volcano-type behavior. Compared with the mechanical mixtures, the BEA/MOR samples displayed higher catalytic activity. The HM with SiO2/Al2O3 molar ratio of 11 deactivated after 60 h reaction though it had high initial activity. The HBEA/MOR with SiO2/Al2O3 molar ratio of 53 showed relatively high catalytic activity and stability.

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Preliminary Study on Synthesis of Salidroside through Glucosylation of D-Glucose and Tyrosol Catalyzed by Microorganism WANG Mengliang*, ZHANG Fang, LIU Diansheng 2006, 27 (3):  233-236.  Abstract ( 2253 )   [Full Text(HTML)] () PDF (241KB) ( 845 )   Salidroside is an important pharmacologically active compound in the traditional Chinese medicinal herb Rhodiola rosea L. In this work, five strains were isolated from soil around the roots of herb, and their catalytic activity for the synthesis of salidroside from D-glucose and tyrosol was tested. F1 strain, which was identified as Aspergillus oryzae, produces the highest amount of salidroside among the five strains. Therefore, its whole cells were used as catalyst for the synthesis of salidroside from D-glucose and tyrosol. The content of salidroside and tyrosol was analyzed by high-performance liquid chromatography. The results show that the highest yield of salidroside is 0.7 g/L under the optimal conditions, i.e., the tyrosol concentration of 5 g/L, reaction time of 48 h, cell concentration of 150 g/L, 30 ℃, and pH of 7. When the tyrosol concentration in the medium is above 5 g/L, the cell growth and the salidroside synthesis are both inhibited. Salidroside is only found inside the cells.

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Macro-Kinetic Study of Water Removal from Ethanol-Water Mixture near Azeotropic Concentration Using Reaction Method WANG Huajun, YANG Bolun*, WU Jiang, LU Shiqing 2006, 27 (3):  237-244.  Abstract ( 2125 )   [Full Text(HTML)] () PDF (447KB) ( 1091 )   A new method of removing water from the ethanol and water mixture near azeotropic concentration was proposed based on isobutylene (IB) hydration-etherification catalyzed by β molecular sieve. The macro-kinetic study of IB hydration-etherification was investigated under the reaction conditions of 2.0 MPa and 313～363 K. The influence of the stirring speed, initial content of water in ethanol, IB/water ratio, and reaction temperature on IB hydration-etherification was investigated. The results indicated that the presence of ethanol favored IB hydration at first, but then it inhibited the reaction. Water had little effect on the etherification between ethanol and IB. The water conversion increased with the IB/water molar ratio and decreased with the initial water content in ethanol; and it increased with the increase of temperature in lower temperature range, but decreased when the temperature was higher than 353 K. The selectivity of IB hydration increased with the initial content of water in ethanol. Under the conditions of 353 K, IB/water molar ratio of 7, and initial water content in ethanol of 10%, the water conversion reached as high as 92.58%. The macro-kinetic model was developed according to the Langmuir-Hinshelwood-Hougen-Watson theory and the experimental results using the Wilson liquid-phase activity to describe the non-ideality of the reactants. The calculated results using the parameters obtained from the hybrid evolutionary algorithm with multi-pattern evolution were in good agreement with the experimental data.

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Effect of Hydrofluoric Acid Post-Treatments on Catalytic Performance of Silicalite-1 for Vapor-Phase Beckmann Rearrangement of Cyclohexanone Oxime TAO Weichuan1,2, MAO Dongsen2*, XIA Jianchao2, CHEN Qingling1,2, HU Ying1 2006, 27 (3):  245-249.  Abstract ( 1920 )   [Full Text(HTML)] () PDF (299KB) ( 817 )   This paper presents a novel modification of silicalite-1 with hydrofluoric acid treatment. Silicalite-1 treated with 0.04%HF solution exhibited remarkable improvements in stability and selectivity for Beckmann rearrangement of cyclohexanone oxime(CHO). Particularly, silicalite-1 catalyst with ammonium nitrate pre-treatment before HF modification showed the best catalytic performance: the conversion of CHO remained nearly 96% after 53 h reaction, and the selectivity for caprolactam during reaction was as high as 96.1%. XRD results showed that all samples hold the MFI structure after HF treatments, but the structural symmetry was changed from orthorhombic to monoclinic. FT-IR spectra revealed that the intensity of silanols, including isolated silanols and associated silanols on silicalite-1 catalysts, decreased severely after HF modification, while the ratio of associated silanols to isolated silanols became much higher. These results indicate that a high ratio of associated silanols to isolated silanols is favorable to the Beckmann rearrangement reaction. However, a 0.45%HF solution used in the modification led to a decrease in activity and selectivity because the arrangement of silicon atoms was greatly changed, which was proved by 29Si MAS NMR. It is inferred that the arrangement of silicon atoms on the surface of silicalite-1 is of significant importance to the catalytic performance of Beckmann rearrangement reaction.

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Preparation and Application of Supported Palladium-Modified Polyimide-Silica Hybrid Membrane for Selective Separation of H2 GU Yongjian, ZHONG Shunhe* 2006, 27 (3):  250-254.  Abstract ( 1791 )   [Full Text(HTML)] () PDF (287KB) ( 659 )   The palladium-modified polyimide-silica (Pd-PI-SiO2) hybrid membrane supported on the kieselguhr-mullite ceramic membrane substrate with a TiO2 transition layer was prepared by the sol-gel method. Infrared spectroscopy, scanning electron microscopy, low temperature N2 adsorption, and gas permeability measurement techniques were used to characterize its structure, micro-surface, pore distribution, and permeability for CH4, H2O, H2, CO2, CO, and N2. The results indicate that a bond is formed between PI and SiO2, and palladium exists in the hybrid membrane as a metallic state with good distribution, which can modify the micro-pore structure of the PI-SiO2 membrane. The pore diameter of the Pd-PI-SiO2 membrane is about 4 nm. The gas permeability measurements show that the N2 permeance flux of this hybrid membrane is 0.2×10-7 mol/(m2•Pa•s), and the separation coefficient of H2/N2 is 542. Palladium has an adsorption effect for hydrogen, which can promote the separation of hydrogen from the gaseous mixture.

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Nanometer β Zeolite Made from Mesoporous Zeolite and Its Hydrocracking Performance CHEN Song1,2*, XU Jie1, YANG Yongrong1, WANG Jingdai1, ZHANG Xiaoping2, ZHANG Kuixi2 2006, 27 (3):  255-258.  Abstract ( 1909 )   [Full Text(HTML)] () PDF (281KB) ( 816 )   MCM-41, a typical mesoporous molecular sieve, was used as silicon source to synthesize β zeolite in hydrothermal process. The β zeolite not only has all characteristics of a microporous zeolite but also inherits some properties of a mesoporous molecular sieve. Its pore diameter and pore volume are 30% and 60%, respectively, higher than that of the β zeolite prepared by the traditional method. Moreover it has smaller crystal grains and much more B acidity. Therefore, when being used as the cracking component in a hydrocracking catalyst, it shows improved catalytic performance. The dynamic activity is promoted by 60% and the middle distillate selectivity is significantly increased by 2.5% compared with the typical commercial hydrocracking catalyst.

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The State of Active Au Species in Au/Fe-O Catalyst during CO Catalytic Oxidation LI Changyan1*, SHEN Yuenian1, HU Ruisheng1, JIA Meilin2, SHENG Shishan3 2006, 27 (3):  259-262.  Abstract ( 2212 )   [Full Text(HTML)] () PDF (325KB) ( 788 )   A series of Au/Fe-O catalysts have been prepared by a co-precipitation method from a mixture of HAuCl4\54H2O and Fe(NO3)3\59H2O. These catalysts exhibit good catalytic activity for CO oxidation. The most active catalyst has 100% CO conversion at room temperature. The calcined catalysts were characterized by X-ray diffraction, X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). TEM observations reveal a homogenous distribution of gold particles between 10 and 15 nm on the iron oxide support. XPS results show that partially oxidized gold species exist in these samples. The difference in binding energies of Au 4f between these samples and bulk gold can be interpreted as that the Au 5d electrons partially flow into the Fe 3d orbit to some extent. So the attraction of nucleus in gold atoms is enhanced, resulting in the increase in the binding energies of Au 4f. This fact reflects that there exists an interaction between the gold nanoparticles and the support. For the CO oxidation on the 10～15 nm Au/Fe-O catalyst, the interaction between nanogold particles and iron oxide has more important influence on catalyst performance than the particle size of nanogold.

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Enzymatic Resolution of (R,S)-Naproxen in Water-Saturated Ionic Liquids XIN Jiaying1,2*, ZHAO Yongjie2, ZHENG Yan1, XIA Chungu2, LI Shuben2 2006, 27 (3):  263-269.  Abstract ( 2149 )   [Full Text(HTML)] () PDF (396KB) ( 950 )   Ionic liquids are a new type of reaction medium for the enzymatic hydrolysis of Naproxen methyl ester because they can not only enhance the water capacity but also promote the solubility of product Naproxen ((S)-(+)-2-(6-methoxy-2-naphthyl) propionic acid). In this paper, a water-saturated ionic liquid system has been selected to increase the conversion and product recovery for the hydrolysis of (R,S)-Naproxen methyl ester. Five imidazolium-based ionic liquids with different anions and organic cations were tested as the reaction medium. These ionic liquids can all facilitate the hydrolysis, but only the reaction in water-saturated ［bmim］PF6 (1-butyl-3-methylimidazolium hexafluorophosphate) proceeds rapidly and gives high conversion. The ionic liquids can slightly dissolve the lipase and make the dissolved lipase inactive. A rough correlation between the solubility of lipase in ionic liquids and its remaining activity is observed. To prevent the dissolving of lipase in ionic liquids, a nonpolar amorphous multiporous silica YWG-C6H5 with a high specific surface area has been used as the support to immobilize the lipase. Enzymatic resolution of (R,S)-Naproxen was conducted in a reactor containing immobilized lipase and water-saturated ［bmim］PF6. After 72 h reaction, 98.2% enantiomeric excess of (S)-Naproxen is obtained with 28.3% conversion. Further increasing the conversion leads to a great loss of the enantiomeric excess for the product. Based on the particular properties of ionic liquids, the reaction medium recycling, product recovery, and water recruiting have been studied. In the batch reaction, the immobilized lipase can be repeatedly used 5 times, and only a slight decrease in the conversion is found.

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Photocatalytic Degradation of Methyl Orange on TiO2 Promoted by Silver YOU Xianfeng1, CHEN Feng1, ZHANG Jinlong1*, HUANG Jiazhen2, ZHANG Lizhong2 2006, 27 (3):  270-274.  Abstract ( 1860 )   [Full Text(HTML)] () PDF (342KB) ( 1443 )   The Ag-TiO2 photocatalyst was prepared by the sol-gel-hydrothermal method. The obtained powder has high surface area and small crystal size. The photocatalytic activity of Ag-TiO2 is enhanced by proper silver loading under UV and visible light irradiation. The optimum content of Ag is 0.15%. However, the photocatalytic activity of Ag-TiO2 decreases with the excessive silver loading. The increment in activity of TiO2 powder enhanced by Ag under visible light irradiation is higher than that under UV light irradiation because of their different mechanisms. Under visible light irradiation, the photoexcited electrons are injected into the conduction band of TiO2 from the dye and then transformed to silver clusters rapidly. Ag clusters accelerate the photocatalytic process through promoting the separation of charges and depressing the recombination of electrons with dye radical cations. The results indicate that the key to improving the activity of dye-sensitized TiO2 system is to efficiently promote the separation of charges and accelerate the reaction of excited electrons and oxygen.

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Hydrogen Production by Aqueous-Phase Reforming of Ethylene Glycol over Pt Catalysts Supported on γ-Al2O3 Modified with Ce and Mg BAI Ying, LU Chunshan, MA Lei, CHEN Ping, ZHENG Yifan, LI Xiaonian* 2006, 27 (3):  275-280.  Abstract ( 2267 )   [Full Text(HTML)] () PDF (407KB) ( 847 )   Pt catalysts supported on γ-Al2O3 modified with Ce or Mg were prepared by impregnation with a H2PtCl6 aqueous solution and used in the hydrogen production by aqueous-phase reforming of ethylene glycol. Catalytic activity testing, N2 physical adsorption, CO chemical adsorption, X-ray diffraction (XRD), and temperature-programmed reduction (TPR) were employed to evaluate the activity, hydrogen selectivity, and physicochemical properties of the catalysts. The results indicate that Pt catalysts supported on γ-Al2O3 modified with Ce or Mg show higher activity than the Pt/γ-Al2O3 catalyst. At the temperature of 498 K and pressure of 2.58 MPa, the conversion of ethylene glycol is increased from 72.3% over Pt/γ-Al2O3 to 100% over Pt/(Ce)γ-Al2O3 or Pt/(Mg)γ-Al2O3, and the selectivity for hydrogen almost reaches 100%. The characteristic peaks attributed to CeO2, Mg-Al layer chemical component, and Mg-Al spinel have been observed besides the γ-Al2O3 peak in the XRD patterns of Pt/(Ce)γ-Al2O3 and Pt/(Mg)γ-Al2O3. The presence of Ce not only increases the dispersion of Pt on the surface of γ-Al2O3, but also improves the adsorption-cracking of ethylene glycol on Pt and water-gas shift reaction; while the presence of Mg neutralizes the acidity of γ-Al2O3, influences the dispersion of PtCl2-6, and inhibits the dehydration of ethylene glycol.

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Electrochemical Durability of Pt/Carbon Nanotube Electrode SHAO Yuyan, YIN Geping*, WANG Jiajun, GAO Yunzhi 2006, 27 (3):  281-284.  Abstract ( 1905 )   [Full Text(HTML)] () PDF (252KB) ( 1030 )   The electrochemical durability of Pt/carbon nanotube (CNT) electrode under potentiodynamic and potentiostatic conditions was investigated. The electrochemical surface area decreased by 18.8% after the electrode was cycled at 0.05～1.2 V for 940 cycles (60 h), while only 5.2% after potentiostatic oxidation at 1.2 V for 60 h. The performance of the Pt/CNT electrode therefore degraded more rapidly under the potentiodynamic condition than that under the potentiostatic condition. X-ray photoelectron spectroscopy analysis showed that the increase in the amount of surface oxygen on the support (multiwalled carbon nanotube) of 1.2 V-oxidized Pt/CNT was more than that on the cyclic voltammetry (CV)-treated one, which indicated that the oxidation degree of MWNT under the potentiostatic condition was higher. X-ray diffraction analysis showed that Pt particle size increased from 3.8 nm to 3.9 and 4.9 nm for 1.2 V-oxidized and CV-oxidized Pt/CNT, respectively. These imply that the increase in Pt particle size, instead of the oxidation of the support, is one of the main reasons for the degradation of Pt/CNT performance.

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Epoxidation of Allyl Alcohol to Glycidol on Ti-MWW Molecular Sieves CHEN Xiaohui*, FAN Zhiyong, QUAN Xia, WEI Kemei 2006, 27 (3):  285-290.  Abstract ( 1912 )   [Full Text(HTML)] () PDF (472KB) ( 733 )   Ti-MWW was prepared by acid treatment and calcination on a lamellar precursor which was synthesized under dynamic hydrothermal crystallization conditions using piperidine as a template, and boric acid as a stucture-supporting agent. The crystallization time is shortened by adding Ti-MWW seeds and increasing stirring rate. Ultraviolet-visible spectra show that the precursor contains tetrahedral and octahedral Ti species. Calcination of the precursor results in a partial condensation of the octahedral Ti to form the anatase phase. The octahedral Ti species belong to a kind of extraframework Ti, which can be removed easily by the acid treatment in a short time. The calcined Ti-MWW contains the anatase when the acid-treated time is too long. The characteristic infrared band at 960 cm-1 is not observed for the Ti-MWW precursor, but it appears in the samples treated by acid. Epoxidation of allyl alcohol with H2O2 on Ti-MWW was studied. Ti-MWW with Si/Ti ratio of 20 and acid treatment for 12～16 h is more effective. The conversation of allyl alcohol is 88.7%, and the selectivity for glycidol is 99% under the reaction conditions of 333 K and 30 min, but the catalytic activity of Ti-MWW decreases when the acid-treated time is too long.