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Chinese Journal of Catalysis
2009, Vol. 30, No. 11
Online: 25 November 2009

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A Simple Method to Improve Electrocatalytic Activity of Pt for Formic Acid Oxidation LI Meichao*;WANG Wuyang;MA Chun’an 2009, 30 (11):  1073-1075.  Abstract ( 2052 )   [Full Text(HTML)] () PDF (382KB) ( 1258 )   A platinum electrode was modified with polypyrrole in the ionic liquid 1-ethylimidazolium trifluoroacetate (PPy-HEImTfa/Pt) using cyclic voltammetry, and its electrocatalytic performance for the oxidation of formic acid was tested. Compared to the Pt electrode, the electrocatalytic activity of PPy-HEImTfa/Pt for the oxidation of formic acid was greatly improved. The complete oxidation of formic acid to CO2 was followed by in situ FT-IR, which showed that with PPy-HEImTfa, formic acid oxidation occurred by a direct pathway mechanism and CO poisoning was much decreased.

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Characterization and Analysis of Carbon Deposited during the Dry Reforming of Methane over Ni/La2O3/Al2O3 Catalysts XU Junke;ZHOU Wei;WANG Jihui;LI Zhaojing;MA Jianxin;* 2009, 30 (11):  1076-1084.  Abstract ( 2180 )   [Full Text(HTML)] () PDF (923KB) ( 1051 )   Ni/La2O3/γ-Al2O3 and Ni/La2O3/α-Al2O3 catalysts were prepared by the incipient wetness impregnation and evaporation methods. Their catalytic properties for the dry reforming of methane without a diluting gas were studied. The fresh and used catalysts and deposited carbon were characterized by H2 temperature-programmed reduction, N2 adsorption-desorption, X-ray diffraction, transmission electron microscopy, thermogravimetry coupled to differential scanning calorimetry, and temperature-programmed hydrogenation. The results showed that there were four carbon species that existed as three types, namely, amorphous (polymeric), filamentous, and graphitic carbon. The amount and type of carbon species on the catalysts depended on the size of Ni particles and texture of the support. The formation and morphology of filamentous carbon were clearly related to the size of Ni particles. Ni particles less than 15 nm suppressed the formation and deposition of filamentous carbons, decreased the amount of carbon deposition, and had more active Cα species, resulting in a better activity and higher stability of the catalysts.

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Nanocast Ordered Mesoporous CeO2 as Support for Highly Active Gold Cata-lyst in CO Oxidation ZHANG Huili;YAN Xiaojie;LI Wencui* 2009, 30 (11):  1085-1090.  Abstract ( 2119 )   [Full Text(HTML)] () PDF (1137KB) ( 1023 )   Ordered mesoporous ceria oxides (CeO2) were synthesized by nanocasting using ordered mesoporous carbon (CMK-3) as the template and cerium nitrate as the CeO2 precursor. The as-prepared materials were characterized by thermogravimetry, elemental analysis, powder X-ray diffraction, transmission electron microscopy, and N2 adsorption. The obtained ceria exhibits a 2-D hexagonal ordered structure with a high surface area of up to 167 m2/g and pore size in the range of 3–5 nm. The carbon template can be completely removed at a temperature as low as 350 oC. Such ceria was then employed as the support for the preparation of gold catalysts by the colloid deposition method. The catalytic activity of the Au/CeO2 catalyst was evaluated in CO oxidation. An enhanced catalytic activity was observed over such a catalyst possibly due to the nano-sized particle and narrow pore size of the ordered mesoporous ceria.

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Effect of Silylation of SBA-15 on Its Supported Cobalt Catalysts for Fischer-Tropsch Synthesis SHAN Yuanyuan;LIEW Kongyong;LI Jinlin* 2009, 30 (11):  1091-1095.  Abstract ( 2197 )   [Full Text(HTML)] () PDF (422KB) ( 949 )   Cobalt catalysts supported on unsilylated and silylated SBA-15 were prepared by incipient wetness impregnation and characterized by elemental analysis, N2 adsorption-desorption, X-ray diffraction, H2 temperature-programmed reduction, H2 temperature-programmed desorption, and oxygen titration. Their catalytic properties for Fischer-Tropsch synthesis were evaluated in a fixed-bed reactor. The results show that the interaction between cobalt and the support was decreased, and the reducibility of the cobalt oxide species was more facile on the silylated Co/SBA-15 catalyst. With increasing (CH3)3SiCl loading, the surface coverage of the trimethylsilyl group increased, and the cobalt cluster size was larger. The higher activity of the silylated 10%Co/SBA-15 catalysts was ascribed to its improved reducibility. The increase in selectivity for C5+ hydrocarbons was attributed to the increase in cobalt cluster size.

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Theoretical Calculation for Reaction Mechanism of Methanol Carbonylation over Pyridine Carbonylic Acid Rhodium Cation JI Wenxin;LIU Xiangyu;JI Yongqiang* 2009, 30 (11):  1096-1100.  Abstract ( 2308 )   [Full Text(HTML)] () PDF (374KB) ( 1008 )   The reaction mechanism of methanol carbonylation catalyzed by pyridine carbonylic acid rhodium cation ([MRh(CO)2]+, where M = pyridine carbonylic acid ligand) catalyst was studied by the ab initio method with the effective core potential approximation in the HF/LANL2DZ level. The results indicated that the whole reaction process was composed of four steps: (1) CH3I oxidative addition; (2) carbonyl rearrangement reaction; (3) carbonyl coordination; (4) reductive elimination of CH3COI. With the consideration of zero-point energy correction, the activation barriers of the four steps were 167.78, 110.67, 0, and 62.94 kJ/mol, respectively. The CH3I oxidative addition was a rate-controlling step, which corresponded to the highest activation barrier. The reaction mechanism of methanol carbonylation catalyzed by [MRh(CO)2]+ was similar to that by [Rh(CO)2I2]-. The reaction activation barriers over [MRh(CO)2]+ were lower than those over [Rh(CO)2I2]- in all four steps.

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Effect of Calcination Temperature on the Reduction Kinetics of Iron-Based Fischer-Tropsch Catalyst WANG Hong;YANG Yong;*;WU Baoshan;XU Jian;WANG Hulin;DING Mingyue;XIANG Hongwei;LI Yongwang 2009, 30 (11):  1101-1108.  Abstract ( 2112 )   [Full Text(HTML)] () PDF (677KB) ( 847 )   A typical iron-based Fischer-Tropsch catalyst was prepared by the combination of precipitation and spray drying. The catalyst was then calcined at different temperatures. The textural properties and the crystal structure of the calcined catalyst samples were characterized by N2 adsorption and Mössbauer effect spectroscopy, respectively. The thermogravimetric analysis was employed to follow the reduction process of the catalysts. The experimental data were then regressed using gas-solid reaction models. The results indicated that the reduction process of the catalysts calcined at 300–600 oC could be described by the same models. The reduction of α-Fe2O3 to Fe3O4 was regressed by the 1-dimentional formation and growth of nuclei model, and the reduction of Fe3O4 to α-Fe was controlled by the 2-dimentional formation and growth of nuclei model. The reduction of the catalyst calcined at 700 oC was influenced by both the formation and growth of nuclei model and the shrinking core model. With the increase of the calcination temperature, the reduction capability of the catalysts decreased and the apparent activation energy increased, being due to the increase of the crystal size and the decrease of the lattice defects in the catalysts.

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Effect of Heat Treatment on the PtRu/C Electrocatalyst Prepared by the Polyol Method YAN Shiyou;SUN Gongquan;*;QI Jing;GAO Yan;XIN Qin; 2009, 30 (11):  1109-1113.  Abstract ( 1927 )   [Full Text(HTML)] () PDF (1170KB) ( 1063 )   The effect of heat treatment on catalytic activity of a PtRu/C electrocatalyst synthesized by the polyol method was investigated by thermogravimetry, on-line mass spectroscopy, X-ray diffraction,?and transmission electron microscopy. The results indicate that abundant species adsorbs on the electrocatalyst surface, which can be effectively removed by heat-treating at 200 oC under inert atmosphere for 2 h. The particle size of the electrocatalyst increases slightly after heat treatment, but the particles remain good dispersion on the carbon support. Electrochemical and direct methanol fuel cell single cell test results indicate that the catalytic activity of PtRu/C for methanol electrooxidation is greatly improved by the heat treatment process.

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Controllable Synthesis of Birnessite and Cryptomelane Types of Manganese Oxide and Their Catalytic Performance DIAO Guiqiang;YU Lin*;SUN Ming;YU Qian;FAN Fangqiang;NA Xiuhui 2009, 30 (11):  1114-1118.  Abstract ( 2042 )   [Full Text(HTML)] () PDF (580KB) ( 1253 )   The birnessite and cryptomelane types of manganese oxide were prepared by the sol-gel method using KMnO4 and glucose. The optimum conditions were investigated by varying different process variables such as c(glucose)/c(KMnO4) ratio, calcination temperature, reaction time, and gel treatment methods. The results of X-ray diffraction and atomic absorption spectroscopy indicated that the crystal phases of manganese oxide were controllable with different gel treatment methods. Under the conditions of c(glucose)/c(KMnO4) = 0.74, t = 20 s and by different gel treatment methods, the birnessite and cryptomelane with high purity and high crystallinity were synthesized. The catalytic performance of both types of manganese oxide for the combustion of dimethyl ether was excellent, but the cryptomelane showed much higher catalytic activity than the birnessite.

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Effect of Different Al and Zr Raw Materials on Catalytic Performance of Cu-Zn-Al-Zr Prepared by Complete Liquid-Phase Technology WANG Jiangyong;HUANG Wei*;GAO Zhihua;LI Junfang 2009, 30 (11):  1119-1124.  Abstract ( 1922 )   [Full Text(HTML)] () PDF (521KB) ( 852 )   Cu-Zn-Al-Zr slurry catalyst samples were prepared from different raw materials of Al and Zr by a complete liquid-phase technology and characterized by X-ray diffraction, X-ray photoelectron spectroscopy, and H2 temperature-programmed reduction. The catalytic performance of the samples for the direct synthesis of dimethyl ether from syngas was evaluated in a slurry reactor. The results indicated that different Al raw materials influenced obviously the catalyst performance, while different Zr raw materials had little effect on the catalyst performance. The activity of the catalyst samples with aluminum isopropoxide as the raw material was significantly higher than that with pseudo-boehmite. The catalyst samples with aluminum isopropoxide as the raw material had good Cu dispersion and strong interaction between Cu and Zr. It was concluded that the existence of trace Na in Al raw materials and the strong interaction between Cu and Zr were the main reasons for good catalytic performance.

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Effect of Precipitation Methods on Catalytic Activity of Ru/CeO2 Catalyst for Ammonia Synthesis LUO Xiaojun;WANG Rong*;LIN Jianxin;WEI Kemei 2009, 30 (11):  1125-1130.  Abstract ( 1982 )   [Full Text(HTML)] () PDF (495KB) ( 984 )   The Ru/CeO2 catalyst was prepared by precipitation methods, including normal precipitation, reverse precipitation, parallel flow precipitation, and deposition-precipitation. The obtained catalysts were characterized by N2 adsorption-desorption, X-ray diffraction, H2 temperature-programmed reduction, CO chemisorption, and X-ray fluorescence spectroscopy. The results showed that the ammonia synthesis activity of the Ru/CeO2 catalyst prepared by normal precipitation was 11.9% at 10 MPa, 10000 h-1,?and 450 oC, which was higher than those obtained by other methods. The residual chloride content in this catalyst was much lower and its cerium was easier to be reduced. Thus the activity of the catalyst prepared using normal precipitation was high.

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Preparation and Catalytic Performance of Bi-Zn Composite Oxide Catalysts for Decomposition of Methyl N-Phenyl Carbamate DAI Yunsheng;WANG Yue;WANG Qingyin;WANG Gongying;* 2009, 30 (11):  1131-1136.  Abstract ( 2104 )   [Full Text(HTML)] () PDF (813KB) ( 1081 )   A series of Bi-Zn composite oxide catalysts were prepared by coprecipitation and used for the synthesis of phenyl isocyanate (PI) by catalytic decomposition of methyl N-phenyl carbamate (MPC). The effects of Bi/Zn molar ratio and calcination temperature on the phase structure and surface properties of the catalysts were investigated by X-ray diffraction, thermogravimetry, and Fourier transform infrared spectroscopy. The addition of Zn can make the crystalline of Bi2O3 change from α phase to β phase with better activity. The Bi-Zn precursor was almost completely decomposed at 500 oC to form Bi2O3 particles and more Bi7.65Zn0.35O11.83 phase. The catalyst with a Bi/Zn molar ratio of 2/1 and the calcination temperature of 500 oC exhibited the highest activity. The MPC conversion and the selectivity for PI were 86.0% and 91.7%, respectively, which was better than the activity of Bi2O3 used alone.

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Structure and Photocatalytic Properties of WO3/TiO2 Composite Film by Mi-croarc Oxidation HE Jian;CAI Qizhou;*;XIAO Feng;LUO Qiang;WANG Lijuan;ZHU Di 2009, 30 (11):  1137-1142.  Abstract ( 1981 )   [Full Text(HTML)] () PDF (2044KB) ( 1121 )   A WO3/TiO2 composite film and a pure TiO2 film were prepared by microarc oxidation in tungsten electrolyte and phosphate electrolyte, respectively. The structure and photophysical properties of the two films were characterized by X-ray diffraction, scanning electron microscopy, UV-Vis spectroscopy, and photoluminescence. The results showed that the two films consisted of a mixture of anatase and rutile, but the ratio of anatase to rutile was different. In addition, WO3 was present in the WO3/TiO2 composite film. The two films had porous structure, but more pores distributed homegeneously on the WO3/TiO2 composite film surface than on the TiO2 film. The WO3/TiO2 composite film showed wider absorption rang while the TiO2 film presented better optical absorption in the UV region. The photoluminescence intensity of the WO3/TiO2 composite film was lower than that of the TiO2 film, which meant that the recombination of photo-generated electrons and holes in the former was less than that in the later. Compared to the TiO2 film, the WO3/TiO2 composite film had higher surface acidity, which increased the adsorption of organics and OH groups on the film surface. More than 85% of rhodanmine was removed by the WO3/TiO2 composite film, whereas only 23% of rhodamine was removed by the TiO2 film for 2 h. The higher photocatalytic removal ratio of the WO3/TiO2 composite film was ascribed to the larger specific surface area, better separation between electrons and holes, and higher surface acidity.

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Propane Oxidative Dehydrogenation over Vanadia Catalysts Supported on Sili-cas with Different Pore Structures MIAO Jianwen;*;SONG Guohua;FAN Yining 2009, 30 (11):  1143-1149.  Abstract ( 2152 )   [Full Text(HTML)] () PDF (588KB) ( 831 )   The state and reactivity of surface oxygen species of mesoporous silica-supported vanadium oxide catalysts for oxidative dehydrogenation of propane have been investigated by microreactor tests combined with in-situ electron spin resonance, temperature-programmed surface reaction, and ultraviolet-visible diffuse reflectance spectroscopy. The pore diameter of the SBA-15, MCM-41, and silica gel supports exert great influences on the dispersion state of VOx species and the catalytic properties of the supported vanadium oxide catalysts. The SBA-15-supported vanadium oxide catalyst has the highest selectivity for propylene because of its larger pore diameter and higher surface area. Surface lattice oxygen species of the VOx/SBA-15 catalyst are main active species for oxidative dehydrogenation of propane to propylene. Highly dispersed VOx species have high catalytic reactivity for oxidative dehydrogenation of propane. CO2 can regenerate the lattice oxygen species of supported vanadium oxide catalysts. The high propylene selectivity for oxidative dehydrogenation of propane by CO2 on supported vanadium oxide catalysts is related to weaker oxidizing effect of CO2, which inhibits the direct C3H8 oxidation and the consecutive oxidation of C3H6 to COx.

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Studies on the Surface Interaction of Supported Metal Oxide Catalysts and Their Applications in the Abatement of Air Pollutant Molecules NO and CO DONG Lin* 2009, 30 (11):  1150-1169.  Abstract ( 2098 )   [Full Text(HTML)] () PDF (7028KB) ( 1155 )   Supported catalysts are widely used in industry and in academic research, and the investigation of the interaction between the dispersed surface components and supports is key to the understanding of the nature of catalytic reactions and the design and development of effective and practical catalysts. This review summarizes some results of our group in this field. The related catalysts include supported metal oxides such as CuO/g-Al2O3, CuO/CexZr1-xO2, and CuO/TixSn1-xO2, and the reactions are mainly focused on the CO oxidation and NO + CO reaction. These mentioned catalysts, prepared by adjusting the loadings of active species, introducing modifiers, and changing preparation conditions, are characterized by normal measurements for solid catalysts in order to explore the functions of each component and monitor the variation of activity in the reactions. It is shown that: (1) the dispersion capacity of metal oxides or halides on the surface of oxide supports and some of their properties can be explained on the basis of the “incorporation model”; (2) the dispersed active species on the different supports or the dispersed active species with different structures on the same support exhibit different redox and catalytic properties, which are resulted from the diversity of their existing states; (3) the results obtained from CO oxidation and NO + CO reactions proceeding on the associated catalysts indicate that it is possible to design catalysts by exploring the relationship among “composition-structure-property”.

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Designed Preparation and Catalysis of Smectite Clay-Based Catalytic Materials TONG Dongshen;XIA Housheng;ZHOU Chunhui* 2009, 30 (11):  1170-1187.  Abstract ( 2171 )   [Full Text(HTML)] () PDF (5362KB) ( 1412 )   This paper presents a critical overview of research progress in the synthesis, properties, structure, and applications of smectite clay-based catalytic materials. The 2:1-type layered structure of smectites, which consists of two Si-O tetrahedral sheets sandwiched by a metal-oxygen octahedral sheet, along with changeable composition of layers, exchangeable cations within interlayers, and intercalation of active species, allows numerous preparation strategies to produce a variety of clay-based catalytic materials. So far the catalytically active species intercalated into the interlayers of clays are metal ions, zero-valent metal, metal oxides, metal complexes, metal sulfides, and carbon, and so forth. The scientific knowledge and accurate control of the distribution and the microstructure of the guest species in the interlayer are critical issues. Such advanced clay-based materials obtained by preparation through designed species within interlayers have provided promising applicability in a number of catalytic reactions such as oxidation, dehydration, hydrogenation, cracking, isomerization, and alkylation. Several key problems and prospects are also remarked.