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Chinese Journal of Catalysis
2007, Vol. 28, No. 2
Online: 25 February 2007

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Medium-Coupled Catalysts Meeting Euro Ⅲ Emission Standards for Gasoline Vehicles WANG Yongjun2, YUAN Shuhua1, SHI Zhonghua1, ZHAO Ming1, GONG Maochu1, LIU Zhongchang3, CHEN Qizhang4, CHEN Yaoqiang1* 2007, 28 (2):  97-99.  Abstract ( 1761 )   [Full Text(HTML)] () PDF (189KB) ( 816 )   The Ce0.5Zr0.4Y0.1O2 oxygen storage material and La-stabilized alumina (La-Al2O3) were prepared. After aging at 1000 ℃ for 5 h, Ce0.5Zr0.4Y0.1O2 maintains superior textual and oxygen storage properties, and La-Al2O3 has superior textual properties. Medium-coupled Pd-Rh monolithic catalysts were prepared by impregnating Ce0.5Zr0.4Y0.1O2 and La-Al2O3 with H2PtCl6 and RhCl3 solutions and then washcoated on the cordierite honeycomb. The medium-coupled catalysts show high low-temperature activity and thermal stability. The results from the emission test of JETTA-MT vehicle show to fulfill Euro Ⅲ requirements.

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Electrocatalytic Synthesis of Propylene Carbonate from CO2 and Propylene Oxide under Mild Conditions ZHANG Li, LUO Yiwen, NIU Dongfang, YU Xindi, LU Jiaxing* 2007, 28 (2):  100-102.  Abstract ( 2060 )   [Full Text(HTML)] () PDF (171KB) ( 1082 )   The electroreduction of CO2 and electrocatalytic synthesis of propylene carbonate (PC) were studied in dimethylformamide (DMF) solvent under mild conditions (p(CO2)=101 kPa, room temperature). CO2 can be electroreduced in DMF-0.1 mol/L tetraethylammonium bromide by cyclic voltammetry. An irreversible one-electron reduction peak of CO2 appeared at -2.1 V vs Ag, indicating that an activated species may be generated. The electrocatalytic synthesis of propylene carbonate from CO2 and propylene oxide in DMF was studied using six different supporting electrolytes. The results showed that supporting electrolytes including Br- acted as both a supporting electrolyte and a catalyst to synthesize propylene carbonate. The selectivity for propylene carbonate was 100%. A proposed mechanism involved the opening of the epoxide ring through a nucleophilic attack by Br-and Mg2+, which formed an intermediate affording propylene carbonate after reaction with the activated CO2.

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Accessibility of Acidic Protons in 12-Phosphotungstic Acid and Its Cesium Hydrogen Salt as Revealed by Solid State NMR Spectroscopy KANG Haixia1*, YANG Jun2* 2007, 28 (2):  103-105.  Abstract ( 2091 )   [Full Text(HTML)] () PDF (173KB) ( 923 )   The accessibility of acidic protons in 12-phosphotungstic acid and its cesium hydrogen salt has been studied by the probe molecule trimethylphosphine and solid state NMR. The experimental results indicate that 2/5 acidic protons in the anhydrous 12-phosphotungstic acid can be accessed by the probe molecules. However, only acidic protons on the surface of the cesium salt of 12-phosphotungstic acid can be accessed by the probe molecules trimethylphosphine.

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Transfer Dehydrogenation of Alcohols over Ceria-Supported Cu, Ir, and Pd Catalysts SONG Wei1, SHI Ruijuan2, LIU Junlong2, ZHAN Ensheng2, LI Zhanshuang1, XU Yide2, SHEN Wenjie2* 2007, 28 (2):  106-108.  Abstract ( 2054 )   [Full Text(HTML)] () PDF (151KB) ( 703 )   Ceria-supported Cu, Ir, and Pd catalysts showed quite promising activity for transfer dehydrogenation of cyclohexanol and 2-octanol to cyclohexanone and 2-octanone, respectively, using styrene as the hydrogen acceptor. The Cu/CeO2 and Pd/CeO2 catalysts were more active than the previously reported Cu and Pd catalysts supported on Al2O3, and Ir/CeO2 exhibited extremely high activity. The reactivity of alcohols decreased in the order 2-octanol>cyclohexanol>benzyl alcohol>1-octanol. The synergetic effect between the metals and CeO2 as well as the effective coupling of dehydrogenation of alcohols and hydrogenation of styrene was responsible for the high catalytic activity.

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The Oxidation Resistance of Tungsten Carbide as Catalyst Support for Proton Exchange Membrane Fuel Cells ZHANG Shengsheng1,2, ZHU Hong1,2*, YU Hongmei2, HOU Junbo2, YI Baolian2, MING Pingwen2 2007, 28 (2):  109-111.  Abstract ( 2194 )   [Full Text(HTML)] () PDF (239KB) ( 1033 )   Electrochemical oxidation of carbon supports for Pt/C catalysts can cause degradation of proton exchange membrane fuel cells (PEMFCs). To improve the oxidation resistance of the catalyst supports, tungsten carbide (WxCy) was investigated as a substitute for carbon supports in PEMFCs. The Pt/C and Pt/WxCy samples were oxidized using the chronoamperometry method. The electrochemical active area of the two samples was measured using cyclic voltammetry. Furthermore, the Pt/C and Pt/WxCy catalysts were applied to single cells to compare their performance degradation after oxidation. As a result, the single cell prepared with Pt/WxCy catalyst showed higher oxidation resistance than the contrastive cell prepared with Pt/C catalyst.

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Reconstruction of Surface Structure of MoBiTeO/SiO2 Catalyst during Propane Selective Oxidation HE Yiming, YI Xiaodong, ZHANG Xiaobing, YING Fang, HUANG Chuanjing, WENG Weizheng*, WAN Huilin* 2007, 28 (2):  112-116.  Abstract ( 1814 )   [Full Text(HTML)] () PDF (371KB) ( 695 )   The catalytic performance of MoBiTeO/SiO2 for selective oxidation of propane to acrolein was investigated, and the catalyst was characterized by means of X-ray powder diffraction, in-situ laser Raman spectroscopy, in-situ laser Raman spectroscopy, and X-ray photoelectron spectroscopy. The results showed that Te-polymolybdate species were the main active phase on the fresh catalyst. Under the conditions of 570 ℃ and C3H8/O2/N2=1.2/1/4, some Te species in the catalyst were reduced to metal Te which was volatilized during the reaction, and therefore the active surface phase of the catalyst was reconstructed, leading to the formation of MoO3 species. Along with the active surface reconstruction, both the conversion of propane and the selectivity for acrolein were increased, which was attributed to the synergistic effect between Te-polymolybdate and MoO3.

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Effect of H2 on Selective Catalytic Reduction of NOx by C3H6 over Ag/Al2O3 and Cu/Al2O3 Catalysts ZHANG Xiuli, HE Hong*, YU Yunbo 2007, 28 (2):  117-123.  Abstract ( 2248 )   [Full Text(HTML)] () PDF (667KB) ( 752 )   The effect of H2 on the selective catalytic reduction (SCR) of NOx by C3H6 was investigated over Ag/Al2O3 and Cu/Al2O3 catalysts by steady in situ diffuse reflectance infrared Fourier transform spectroscopy. The presence of H2 might accelerate the partial oxidation of C3H6 over Ag/Al2O3 to enolic species and acetate. The enolic species can react easily with nitrates to form surface -[KG-20x]NCO species. An enhancement of enolic species formation promoted the SCR of NOx over Ag/Al2O3 in the presence of H2. As for the Cu/Al2O3 catalyst, the addition of H2 did not influence the partial oxidation of C3H6 to acetate but inhibited apparently the formation of nitrates, and subsequently blocked the reaction between acetate and nitrates to form the key -[KG-20x]NCO species. This led to the deactivation of Cu/Al2O3 in the SCR of NOx in the presence of H2.

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Pd/V2O5-SiO2 Catalyst for Oxidative Dehydrogenation of Isobutane with CO2 to Isobutene WANG Maogong, ZHONG Shunhe* 2007, 28 (2):  124-130.  Abstract ( 2068 )   [Full Text(HTML)] () PDF (562KB) ( 736 )   A series of supported Pd catalysts were prepared by incipient impregnation using a V2O5-SiO2 surface complex prepared by surface modification as the support. Their structure, valence states, chemisorption properties for isobutane, and catalytic activity for isobutane partial oxidation with CO2 were characterized by N2 adsorption, X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, temperature-programmed desorption, chemisorption-infrared spectroscopy, and microreactor techniques. The results showed that the lattice oxygen of V[KG-45x]=[KG-20x]O was the active site on the Pd/V2O5-SiO2 catalyst, and the valence of vanadium in the V[KG-45x]=[KG-20x]O was positive 5. Isobutane was chemisorbed on the lattice oxygen of V[KG-45x]=[KG-20x]O through the H atoms in -[KG-20x]CH3 and -[KG-20x]CH of i-C4H10. Carbon dioxide was chemisorbed horizontally on the catalyst through the synergetic effect of Pd and V4+. The V5+←[KG-*4]→V4+ couple played a key role in the redox mechanism of the catalytic reaction. In the presence of Pd/25%V2O5-SiO2 and under the conditions of 525 ℃, 0.1 MPa, CO2/i-C4H10 volume ratio of 1, and mixed gas space velocity of 1200 h-1, 22.8% conversion of isobutane and 89.1% selectivity for isobutene were achieved.

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H2 Production from Steam Reforming of High Energy Density Motor Fuel with Sulfu Ⅰ. Preparation, Characterization, and Sulfur Tolerance of Pt/Ce0.8Gd0.2O1.9 Catalyst CHEN Jinchun, LIU Ye, LU Yong*, XUE Qingsong, GAO Lida, WANG Ya, HE Mingyuan 2007, 28 (2):  131-136.  Abstract ( 1935 )   [Full Text(HTML)] () PDF (415KB) ( 912 )   A high sulfur tolerant Pt catalyst was prepared using a fluorite-type Ce0.8Gd0.2O1.9[KG10x](CGO) oxide as the support that was synthesized by the citric acid sol-gel method. Sulfur tolerance of the catalyst was tested for the steam reforming of isooctane at 750 ℃ and isooctane WHSV of 1.0 h-1 with a steam/carbon molar ratio of 3 using thiophene as the sulfur source. The catalyst calcined at 800 ℃ maintained its activity and selectivity in the entire 100 h test with 300 μg/g or more sulfur, whereas the catalyst calcined at 600 ℃ lost its activity slowly in this course because of both sulfur poisoning and its poor thermal stability. Temperature-programmed reduction and X-ray diffraction analyses, together with comparison of the activity of Pt/CGO with Ni/CGO and Pt/Al2O3, showed that the synergistic effect between CGO oxide and Pt at the interface existed while being enhanced and consolidated with the calcination treatment at 800 ℃, which made Pt immune to sulfur poison and active to convert thiophene sulfur into H2S. In addition, sulfur balance measurements together with diffuse reflectance infrared Fourier transform spectroscopy and microcoulomb titration for surface sulfur-containing species on the used catalyst suggested that thiophene sulfur was completely converted into H2S, probably complying with a redox mechanism.

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Preparation of Nano-Ru-Embedded Catalyst and Its Catalytic Performance for Water-Gas Shift Reaction GUO Xiaoyong, HUA Nanping, DU Yukou, YANG Ping* 2007, 28 (2):  137-142.  Abstract ( 1992 )   [Full Text(HTML)] () PDF (514KB) ( 795 )   RuO2 nanoparticles with an average diameter of 4.9 nm were prepared using the sol-gel method. Ru-based embedded catalysts were prepared by one-step deposition using MgAl2O4 spinel as the support. The nanoparticles and the catalysts were characterized by transmission electron microscopy, scanning electron microscopy, and X-ray diffraction. The results showed that the Ru nanoparticles were evenly distributed in the MgAl2O4 spinel support. The as-prepared embedded catalyst showed high activity for the water-gas shift reaction, and the Ru nanoparticles contacted with reactant molecules through the pores formed during the calcination of the catalyst. The addition of an appropriate amount of K2O and La2O3 promoters effectively improved the catalyst activity.

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Preparation and Characterization of Ni2P/SiO2-Al2O3 and Its Catalytic Performance for Hydrodesulfurization of 4,6-Dimethyldibenzothiophene SONG Limin, LI Wei*, ZHANG Minghui, TAO Keyi 2007, 28 (2):  143-147.  Abstract ( 1957 )   [Full Text(HTML)] () PDF (448KB) ( 790 )   A series of SiO2-Al2O3 composite supports were prepared by simple hydrolysis and deposition of Na2SiO3•9H2O on macropore Al2O3. Ni2P/SiO2-Al2O3 catalysts were prepared by treating amorphous Ni alloys supported on SiO2-Al2O3 with phosphine at a low temperature. The as-obtained samples were characterized by X-ray diffraction, infrared spectroscopy, scanning electron microscopy, inductively coupled plasma-atomic emission spectroscopy, and N2 adsorption. The presence of SiO2 decreased the amount of four-complexing Al3+ ions on the surface of Al2O3 and weakened the strong interaction between the Al2O3 support and Ni2P. The SiO2-Al2O3 composite support still kept the pore structure of macropore Al2O3 when the content of SiO2 was proper in the composite supports. Ni2P/SiO2-Al2O3 catalysts showed good activity for the hydrodesulfurization of 4,6-dimethyl-dibenzothiophene under the experimental conditions.

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Deactivation Mechanism of Nanosized Gold Catalysts Stored in Ambient Air WANG Donghui1*, DONG Tongxin1, SHI Xicheng1, HAO Zhengping2 2007, 28 (2):  148-152.  Abstract ( 2374 )   [Full Text(HTML)] () PDF (369KB) ( 1180 )   A nanosized 2.5%Au/ZnO catalyst was prepared using the coprecipitation method at low temperature. The deactivation mechanism of the catalyst stored in ambient air was investigated using scanning transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and thermogravimetric analysis. The deactivation of the catalyst was partially reversible, and two factors interrelated the deactivation. One was the agglomeration of nanosized gold particles, which caused the irreversible deactivation. The other was the accumulation of carbonates on the catalyst surface, leading to the reversible deactivation. The carbonates could be decomposed when the deactivated catalyst was calcined at high temperature.

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A Preparation Method to Obtain Porous Anatase TiO2 Films at Room Temperature SHEN Qianhong1, CAI Zhenqian1, GAO Jiwei1,2, YANG Hui1,2* 2007, 28 (2):  153-157.  Abstract ( 2366 )   [Full Text(HTML)] () PDF (385KB) ( 717 )   Anatase TiO2 films were prepared from a solution of polystyrene spheres and anatase TiO2 colloidal particles by a dip-coating technique. Polystyrene spheres in the films were then preferentially dissolved in toluene, and porous anatase TiO2 films were obtained. The porosity of the films induces effective adsorption of rhodamine B on the TiO2 surface, and thus the photocatalytic activity is enhanced. This preparation method has two advantages. First, the annealing step in typical process is avoided and various substrates can be used. Second, it is facile to control the aperture of the porous films by adding as-prepared polystyrene spheres with different diameters.

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Mechanism of Acetylene Adsorption on ZSM-5 Zeolites and Characteristics of the Surface Species YU Qing, WANG Xinping*, CHEN Jing, JIA Cuiying 2007, 28 (2):  158-162.  Abstract ( 2005 )   [Full Text(HTML)] () PDF (380KB) ( 964 )   Adsorption and desorption of acetylene on HZSM-5 and NaZSM-5 zeolites were investigated in the presence of trace water. The results showed that saturated adsorption of acetylene on NaZSM-5 was about five times as much as that on HZSM-5 at 80 ℃, but little acetylene could bear the temperature up to 200 ℃, which is in contrast to the strong adsorption of acetylene on HZSM-5. Based on the FT-IR results characterizing the adsorption states of acetylene on the zeolites as well as their evolution with increasing temperature, a mechanism of acetylene adsorption on ZSM-5 zeolites was proposed that acetylene reacts with the water adsorbed on Bronsted acid sites to form vinyl alcohol. The latter is converted to carbonium ions bound to Al[KG-45x]-[KG-20x]O-[KG-45x]-[KG-20x]Si, corresponding to the strongly adsorbed species on HZSM-5. On NaZSM-5, acetylene reacts with the water adsorbed on Na+ sites to form vinyl alcohol bound to the cations in zeolite through static attraction, corresponding to the weakly adsorbed species. Being different from the case of HZSM-5, the species on NaZSM-5 can not be further activated because they are decomposed to acetylene and desorbed with increasing temperature.

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Effect of Preparation Method and Calcination Temperature on Low-Temperature CO Oxidation over Co3O4/CeO2 Catalyst SHAO Jianjun1,2, ZHANG Ping1, TANG Xingfu2, ZHANG Baocai2, SONG Wei2, XU Yide2, SHEN Wenjie2* 2007, 28 (2):  163-169.  Abstract ( 2180 )   [Full Text(HTML)] () PDF (547KB) ( 688 )   Co3O4/CeO2 mixed oxides were prepared by coprecipitation-oxidation, homogeneous precipitation, and complexation-combustion methods. The catalysts were used to catalyze low-temperature CO oxidation under dry and humid conditions. The Co3O4/CeO2 catalyst prepared by the coprecipitation-oxidation method followed by calcination at 538 K exhibited excellent activity and good resistance to water vapor poisoning. Remarkably, a CO conversion of 99% was achieved at a temperature as low as 196 K and was maintained more than 400 min under the dry condition. When the reaction was carried out at 298 K, a CO conversion of 94% was obtained after running the reaction for 2400 min. Even when 3.1% steam was added, a CO conversion of 79% could be kept after 2400 min time-on-stream at 383 K. It is suggested that the strong interaction between Co3O4 and CeO2 is closely related to the preparation route and the calcination temperature and plays a crucial role in the CO oxidation over the Co3O4/CeO2 catalyst.

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Comparative Study of Structure and Catalytic Properties of Ti-HMS and TS-1 Molecular Sieves JIN Changzi, LI Gang*, WANG Xiangsheng, WANG Yun, LIU Hai’ou 2007, 28 (2):  170-174.  Abstract ( 1984 )   [Full Text(HTML)] () PDF (387KB) ( 766 )   The mesoporous molecular sieve Ti-HMS was synthesized using long-chain dodecylamine as the template. The crystallization process, structural properties, and catalytic performance of Ti-HMS were compared with that of microporous molecular sieve TS-1 prepared by modified classical synthesis. With the increase in crystallization temperature, the relative crystallinity of Ti-HMS decreased, and the pH value of the mother liquid changed little during the crystallization process, which might be attributed to its crystallization mechanism differed from TS-1. Unlike TS-1 having typical crystalline character, the Ti-HMS molecular sieve exhibited amorphous characteristics except for the lattice fringe in some area of its HRTEM image. The UV-Vis spectrum indicated that the framework Ti species of Ti-HMS were in distorted tetrahedral environment. In oxidation of bulky sulfur compounds such as benzothiophene, the Ti-HMS molecular sieve had very high catalytic activity, with a benzothiophene removal rate of about 100%. However, TS-1 was inactive for this reaction because of the diffusion restriction. In addition, Ti-HMS showed lower activity than TS-1 for selective oxidation of small molecular reactants owing to its weaker oxidative ability and lower shape selective catalytic performance.

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Immobilization of Serratia marcescens Lipase and Catalytic Resolution of Trans-3-(4’-methoxyphenyl)glycidic Acid Methyl Ester LONG Zhangde1,2, XU Jianhe1*, PAN Jiang1 2007, 28 (2):  175-179.  Abstract ( 2411 )   [Full Text(HTML)] () PDF (321KB) ( 901 )   Seven carriers were investigated for immobilization of the lipase from Serratia marcescens ECU1010, and diatomite and Eupergit C were found to be ideal supports. The thermal and storage stability of the lipase was significantly improved after being immobilized onto these two supports. After heating at 50 ℃ for 6 h, only a small decrease in the activity was observed for the diatomite-adsorbed lipase. About 50% of the initial activity was retained when the two immobilized enzyme samples were storaged at 4 ℃ for 180 days. Operational stability tests indicated that the half-life of the lipase immobilized on Eupergit C was about 2-fold longer than that of the diatomite-immobilized lipase. The crosslinking with glutaraldehyde had no significant effect on the activity of the Eupergit C-immobilized lipase, whereas the reusability of the crosslinked diatomite-immobilized enzyme was slightly improved. Using the crosslinked diatomite-immobilized lipase, an up-scaled bioresolution of (±)-3-(4’-methoxyphenyl)glycidic acid methyl ester ((±)-MPGM) was performed in a 500-ml emulsion reactor with 200 ml biphasic solution (toluene∶water=1∶1) at 30 ℃ and 0.5 mol/L of (±)-MPGM in toluene. After 5 batches of reaction, crystalline (2R,3S)-(-)-MPGM with a chemical purity of 100% and optical purity of>99% enantiomeric excess was obtained in a yield of 37.2%.

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Density Functional Theory Study on Structure of Molybdenum Carbide Loaded on MCM-22 Zeolite and Mechanism for Methane Activation ZHU Hongyuan1, ZHANG Yuan1, ZHOU Danhong1,2*, GUAN Jing2, BAO Xinhe2* 2007, 28 (2):  180-186.  Abstract ( 2330 )   [Full Text(HTML)] () PDF (418KB) ( 879 )   Density functional theory was employed to study the geometric and electronic structure of molybdenum carbide loaded on MCM-22 zeolite and predict the mechanism for CH4 activation. Two models of active center, Mo(CH2)2[KG10x](Model A) and Mo(CH)CH2[KG10x](Model B), were designed; they were located on the T4 site of the supercage in MCM-22 zeolite. The geometry optimization and electronic structure analysis of the models were performed based on 3T cluster model. The optimized geometry showed that the Mo connected with CH2 terminal group by double bond (bond length 0.18[KG-45x]-[KG-20x]0.19 nm) and with CH terminal group by triple bond (bond length 0.17 nm). The natural bond orbital calculation revealed that the Mo was bonded to framework oxygen through σ bond. In terms of the composition and the energy of the frontier orbitals, it was suggested that the CH4 activation on Mo carbide active center would happen between the HOMO of CH4 molecule and the LUMO of Mo carbide. Namely, electrons preferred to transfer from the σ-orbital of C[KG-45x]-[KG-20x]H bond to the π*-orbital of Mo[KG-45x]-[KG-20x]C bond. After heterogenous splitting of C[KG-45x]-[KG-20x]H bond, the H3C- group was bonded to Mo and the H+ was bonded to C in Mo carbide species. The calculated activation energy on Model [WTHZ]A[WTBZ] was 119.97 kJ/mol. On Model [WTHZ]B[WTBZ], there were two possible pathways, in which the hydrogen in CH4 could attach to CH2 and CH terminal groups. The corresponding activation energy was 91.37 and 79.07 kJ/mol, respectively.