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2006, Vol. 15, No. 3　Online: 2006-09-30

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Modified Ceria-Zirconia Fluorite-Like Catalysts for the Combustion of Methane Tatiana Kuznetsova;Vladislav Sadykov;Lubsan Batuev;Ella Moroz;Elena Burgina;Vladimir Rogov;Vladimir Kriventsov;Dmitrii Kochubey 2006, 15(3): 149-163.  DOI: 摘要 ( 9900 )   PDF   For dispersed ceria-zirconia-based solid solutions prepared via the polymerized complex method and annealed at 700 ‰, effects of bulk doping by Ca, Mn, Co, Bi or Nb cations and surface modification by Mn and Pt on their structural features, surface/bulk oxygen reactivity and catalytic activity in methane combustion are considered. With up to 20 mol% doping, a structural type of ho- mogeneous solid solutions of anion-deficient fluorite with disordered anion vacancies is formed. Doping by transition metal cations or Pt increases the mobility and reactivity of the surface/bulk oxygen. A broad variation in specific rates of methane combustion for the studied systems was observed, suggesting structural sensitivity of this reaction. In general, there is no universal relationship between the oxygen mo- bility, the reactivity and the catalytic activity in methane combustion, which is explained by the factor of specific methane activation on surface active sites. For the Pt-promoted samples, Pt efficiency in methane activation depends on the Pt-support interaction, and the most favorable ones being mixed Pt/MnOx and Pt/NbOx clusters on the surface of the supports that exhibit high lattice oxygen mobilities.

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Titanium-Containing Mesoporous Materials: Synthesis and Application in Selective Catalytic Oxidation Jie Li;Chunhui Zhou;Huali Xie;Zhonghua Ge;Liangcai Yuan;Xiaonian Li 2006, 15(3): 164-177.  DOI: 摘要 ( 12920 )   PDF   Titanium-containing mesoporous molecular sieves are of great significance in selective cat- alytic oxidation processes with bulky molecules. Recent researches and developments on the designing and synthesis of Ti-containing mesoporous materials have been reviewed. Various strategies for the prepa- ration of Ti-containing mesoporous materials, such as direct synthesis and post-synthesis, are described. Modifications of Ti-containing mesoporous materials by surface-grafting and atom-planting are also dis- cussed. All approaches aimed mainly at the improving of the stability, the hydrophobicity, and mostly the catalytic activity. Structural and mechanistic features of various synthetic systems are discussed. Ti- containing mesoporous materials in liquid phase catalytic oxidation of organic compounds with H2O2 as an oxidant is briefly summarized, showing their broad utilities for green synthesis of fine chemicals by catalytic oxidative reactions.

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Influence of Preparation Conditions on the Catalytic Performance of MoNx/SBA-15 for Ammonia Decomposition Hongchao Liu;Hua Wang;Jianghan Shen;Ying Sun;Zhongmin Liu 2006, 15(3): 178-180.  DOI: 摘要 ( 8975 )   PDF   The influence of preparation conditions (e.g. H2-N2 ratios, final nitriding temperatures) on the performance of MoNx/SBA-15 catalysts for ammonia decomposition was investigated. The variation of catalytic activity with H2-N2 ratios may be attributed to the variation of surface compositions and particle sizes of the active components. The variation of nitriding temperatures leads to the formation of molyb- denum nitride domains of varying compositions, which are responsible for the difference in their catalytic performance with respect to ammonia decomposition. At 923 K, ammonia could be completely decom- posed using 15800 ml/h·g-cat of GHSVNH3 , which shows high performance for the catalytic decomposition of ammonia.

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Carbon-Supported Silver Catalysts for CO Selective Oxidation in Excess Hydrogen Limin Chen;Ding Ma;Barbara Pietruszka;Xinhe Bao 2006, 15(3): 181-190.  DOI: 摘要 ( 8431 )   PDF   Carbon materials were used as supports for Ag catalysts that are prepared using the con- ventional wet impregnation method, and their catalytic properties for CO selective oxidation in excess hydrogen at temperatures below 483 K were tested. A variety of techniques, e.g. N2 adsorption, XPS, TPD, UV-Vis DRS, TEM and SEM, were used to determine the influence of physical and chemical prop- erties of the carbon on the properties of Ag catalyst. It was found that defects on the carbon surface served as nucleation sites for silver ions, while functional groups on carbon surface induced their reduc- tion to the metallic form. The formation of silver particles on carbon was governed by homogeneous and/or heterogeneous nucleation during the impregnation and subsequent activation processes. The best catalytic performance was obtained with a Ag/carbon black catalyst with a uniform size distribution of silver nanoparticles (about 12 nm), moderate BET surface area (with a mesoporous structure), and a lim- ited amount of carbon-oxygen groups. The research indicates that carbon materials are potentially good supports for silver catalysts for preferential oxidation of CO in excess hydrogen.

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Dual-Bed Catalytic System for Direct Conversion of Methane to Liquid Hydrocarbons N. A. S. Amin;Sriraj Ammasi 2006, 15(3): 191-202.  DOI: 摘要 ( 9619 )   PDF   A dual-bed catalytic system is proposed for the direct conversion of methane to liquid hydrocarbons. In this system, methane is converted in the first stage to oxidative coupling of methane (OCM) products by selective catalytic oxidation with oxygen over La-supported MgO catalyst. The second bed, comprising of the HZSM-5 zeolite catalyst, is used for the oligomerization of OCM light hydrocarbon products to liquid hydrocarbons. The effects of temperature (650-800 ℃), methane to oxygen ratio (4-10), and SiO2/Al2O3 ratio of the HZSM-5 zeolite catalyst on the process are studied. At higher reaction temperatures, there is considerable dealumination of HZSM-5, and thus its catalytic performance is reduced. The acidity of HZSM-5 in the second bed is responsible for the oligomerization reaction that leads to the formation of liquid hydrocarbons. The activities of the oligomerization sites were unequivocally affected by the SiO2/Al2O3 ratio. The relation between the acidity and the activity of HZSM-5 is studied by means of TPD-NH3 techniques. The rise in oxygen concentration is not beneficial for the C5+ selectivity, where the combustion reaction of intermediate hydrocarbon products that leads to the formation of carbon oxide (CO+CO2) products is more dominant than the oligomerization reaction. The dual-bed catalytic system is highly potential for directly converting methane to liquid fuels.

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States of Carbon Nanotube Supported Mo-based HDS Catalysts Hongyan Shang;Chenguang Liu;Yongqiang Xu;Jieshan Qiu;Fei Wei 2006, 15(3): 203-210.  DOI: 摘要 ( 10971 )   PDF   The dispersion of the active phase and loading capacity of the Mo species on carbon nanotube (CNT) was studied by the XRD technique. The reducibility properties of Co-Mo catalysts in the oxide state over CNTs were investigated by TPR, while the sulfided Co-Mo/CNT catalysts were characterized by means of the XRD and LRS techniques. The activity and selectivity with respect to the hydrodesulfur- ization (HDS) performances on carbon nanotube supported Co-Mo catalysts were evaluated. It was found that the main active molybdenum species in the oxide state MoO3/CNT catalysts were MoO2, but not MoO3, as generally expected. The maximum loading before the formation of the bulk phase was lower than 6% (percent by mass, based on MoO3). TPR studies revealed that the active species in the oxide state Co-Mo/CNT catalysts were reduced more easily at relatively lower temperatures in comparison to those of the Co-Mo/γ-Al2O3 catalysts, indicating that the CNT support promoted or favored the reduction of the active species. The active species of a Co-Mo-0.7/CNT catalyst were more easily reduced than those of the Co-Mo/CNT catalysts with Co/Mo atomic ratios of 0.2, 0.35, and 0.5, respectively, suggesting that the Co/Mo atomic ratio has a great effect on the reducibility of the active species. It was found that the incorporation of cobalt improved the dispersion of the molybdenum species on the support, and a phenomenon of mobilization and re-dispersion had occurred during the sulfurization process, resulting in low valence state Mo3S4 and Co-MoS2.17 active phases. HDS measurements showed that the Co-Mo/CNT catalysts were more active than the Co-Mo/γ-Al2O3 ones for the desulfurization of DBT, and the hy- drogenolysis/hydrogenation selectivity of the Co-Mo/CNT catalysts was also much higher than those of the Co-Mo/γ-Al2O3. The Co-Mo/CNT catalyst with a Co/Mo atomic ratio of 0.7 showed the highest activity, whereas the catalyst with a Co/Mo atomic ratio of 0.35 had the highest selectivity.

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Preparation and Characterization of Carbon Nanotubes-Coated Cordierite for Catalyst Supports Jianmei Wang;Rong Wang;Xiujin Yu;Jianxin Lin;Feng Xie;Kemei Wei 2006, 15(3): 211-216.  DOI: 摘要 ( 7938 )   PDF   The carbon nanotubes-coated cordierite (CNTs-cordierite) was fabricated by pyrolysis of ethine on cordierite with iron catalyst, which was penetrated into the cordierite substrate by vacuum im- pregnation. The cordierite substrate, carbon naontubes, and CNTs-cordierite were characterized by SEM, TEM/HREM, BET, and TGA. The results show that the carbon nanotubes were distributed uniformly on the surface of cordierite. A significant increase in BET surface area and pore volume was observed, and a suitable pore-size distribution was obtained. On the CNTs-cordierite, carbon nanotubes penetrated into the cordierite substrate, which led to a remarkable stability of the CNTs against ultrasound maltreatment. Growth time is an important factor for thermostability and texture of the sample. The mass increased but the purity decreased with the growth time, which caused the exothermic peak shift to low temperature, and the corresponding full width half maximum (FWHM) of the peak in DTG increased.

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Poly-Acrylic Acid Derivatives as Diesel Flow Improver for Paraffin-Based Daqing Diesel Cuiyu Jiang;Ming Xu;Xiaoli Xi;Panlun Qi;Hongyan Shang 2006, 15(3): 217-222.  DOI: 摘要 ( 9730 )   PDF   Since the diesel products from paraffin-based Daqing crude oil showed low sensitivity to certain commercial diesel pour point depressant (PPDs) that resulted from the high content of paraffin, certain poly-acrylic acid derivatives (PADE) with -COOR, -COOH and -CONHR, -COO-NH3+R groups by molecular design on the mechanics of diesel; PPDs were synthesized and evaluated as cold flow improver for Daqing 0# diesel in this paper. The pure PADE was superior to the commercial PPDs and displayed a substantial ability of wax crystals dispersion. There was a synergistic effect among the PADE and T1804 and secondary amine. The synergism clearly improved the low temperature performance of Daqing diesel products and could reduce the cold filter plugging point of 0# diesel by 6~7 ℃.

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Adsorption of Carbon Dioxide on Activated Carbon Bo Guo;Liping Chang;Kechang Xie 2006, 15(3): 223-229.  DOI: 摘要 ( 13590 )   PDF   The adsorption of CO2 on a raw activated carbon A and three modified activated carbon samples B, C, and D at temperatures ranging from 303 to 333 K and the thermodynamics of adsorption have been investigated using a vacuum adsorption apparatus in order to obtain more information about the effect of CO2 on removal of organic sulfur-containing compounds in industrial gases. The active ingredients impregnated in the carbon samples show significant influence on the adsorption for CO2 and its volumes adsorbed on modified carbon samples B, C, and D are all larger than that on the raw carbon sample A. On the other hand, the physical parameters such as surface area, pore volume, and micropore volume of carbon samples show no influence on the adsorbed amount of CO2. The Dubinin-Radushkevich (D- R) equation was the best model for fitting the adsorption data on carbon samples A and B, while the Freundlich equation was the best fit for the adsorption on carbon samples C and D. The isosteric heats of adsorption on carbon samples A, B, C, and D derived from the adsorption isotherms using the Clapeyron equation decreased slightly increasing surface loading. The heat of adsorption lay between 10.5 and 28.4 kJ/mol, with the carbon sample D having the highest value at all surface coverages that were studied. The observed entropy change associated with the adsorption for the carbon samples A, B, and C (above the surface coverage of 7 ml/g) was lower than the theoretical value for mobile adsorption. However, it was higher than the theoretical value for mobile adsorption but lower than the theoretical value for localized adsorption for carbon sample D.

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Radial Basis Function Neural Networks-Based Modeling of the Membrane Separation Process: Hydrogen Recovery from Refinery Gases Lei Wang;Cheng Shao;Hai Wang;Hong Wu 2006, 15(3): 230-234.  DOI: 摘要 ( 8395 )   PDF   Membrane technology has found wide applications in the petrochemical industry, mainly in the purification and recovery of the hydrogen resources. Accurate prediction of the membrane separation performance plays an important role in carrying out advanced process control (APC). For the first time, a soft-sensor model for the membrane separation process has been established based on the radial basis function (RBF) neural networks. The main performance parameters, i.e, permeate hydrogen concentration, permeate gas flux, and residue hydrogen concentration, are estimated quantitatively by measuring the operating temperature, feed-side pressure, permeate-side pressure, residue-side pressure, feed-gas flux, and feed-hydrogen concentration excluding flow structure, membrane parameters, and other compositions. The predicted results can gain the desired effects. The effectiveness of this novel approach lays a foundation for integrating control technology and optimizing the operation of the gas membrane separation process.

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Synthesis and Application of Carbon Nanotubes Qun Zeng;Zhenhua Li;Yuhong Zhou 2006, 15(3): 235-246.  DOI: 摘要 ( 7929 )   PDF   Owing to the unique structure, the superior physical and chemical properties, the super strong mechanical performances, and so on, carbon nanotubes have attracted the attention of researchers all over the world. In this article, the basic properties and the main production processes of carbon nanotubes are introduced in brief, and the progress of applied research for carbon nanotubes is reviewed.