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2007, Vol. 16, No. 2　Online: 2007-06-30

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Modeling of Fischer-Tropsch Synthesis in a Slurry Reactor with Water Permeable Membrane Fabiano A.N. Fernandes 2007, 16(2): 107-114.  DOI: 摘要 ( 11376 )   PDF   Fischer-Tropsch synthesis is an important chemical process for the production of liquid fuels and olefins. In recent years, the abundant availability of natural gas and the increasing demand of olefins, diesel, and waxes have led to a high interest to further develop this process. A mathematical model of a slurry membrane reactor used for syngas polymerization was developed to simulate and compare the maximum yields and operating conditions in the reactor with that in a conventional slurry reactor. The carbon polymerization was studied from a modeling point of view in a slurry reactor with a water permeable membrane and a conventional slurry reactor. Simulation results show that different parameters affect syngas conversion and carbon product distribution, such as the hydrogen to carbon monoxide ratio, and the membrane parameters such as membrane permeance.

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Fischer-Tropsch Reaction Kinetics of Cobalt Catalyst in Supercritical Phase Abdullah Irankhah;Ali Haghtalab*;Ebrahim Vasheghani Farahani;Kambiz Sadaghianizadeh 2007, 16(2): 115-120.  DOI: 摘要 ( 12536 )   PDF   Fischer-Tropsch synthesis under supercritical phase condition was examined in a continuous and a high-pressure fixed bed reactor by employing a cobalt catalyst (Co-Ru/ γ-Al2O3). An integral reactor model involving Fischer-Tropsch reaction kinetics in the supercritical fluid n-hexane was used to describe the overall performance. On the basis of Langmuir-Hinshelwood-Hougen-Watson (LHHW) model, the reaction rate constants were obtained for the rate equations of CO conversion to CH4 formation under supercritical conditions.

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Oxidative Coupling of Methane over Lithium Doped (Mn+W)/SiO2 Catalysts A. Malekzadeh*;A. Khodadadi;A. K. Dalai;M. Abedini 2007, 16(2): 121-129.  DOI: 摘要 ( 11775 )   PDF   Modification and performance of Li induced silica phase transition of (Mn+W)/SiO2 catalyst, under reaction conditions of oxidative coupling of methane (OCM), have been investigated employing textural characterizations and redox studies. Stability and precrystalline form of fresh Li induced silica phase transition catalyst depend on the Li loading. A catalyst, with high lithium loading, destabilizes on OCM stream. This destabilization is not due to Li evaporation at OCM reaction conditions. α-cristobalite is proposed to be an intermediate in the crystallization of amorphous silica into quartz in the Li-induced silica phase transition process. However, the type of crystalline structure was found to be unimportant with regard to the formation of a selective catalyst. Metal-metal interactions of Li-Mn, Li-W and Mn-W, which are affected during silica phase crystallization, are found to be critical parameters of the trimetallic catalyst and were studied by TPR. Role of lithium in Li doped (Mn+W)/SiO2 catalyst is described as a moderator of the Mn-W interaction by involving W in silica phase transition. These interactions help in the improvement of transition metal redox properties, especially that of Mn, in favor of OCM selectivity.

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Effect of Al2O3 Binder on the Precipitated Iron-Based Catalysts for Fischer-Tropsch Synthesis Hai-Jun Wan;Bao-Shan Wu;Xia An;Ting-Zhen Li;Zhi-Chao Tao;Hong-Wei Xiang*;Yong-Wang Li 2007, 16(2): 130-138.  DOI: 摘要 ( 9865 )   PDF   A series of iron-based Fischer-Tropsch synthesis (FTS) catalysts incorporated with Al2O3 binder were prepared by the combination of co-precipitation and spray drying technology. The catalyst samples were characterized by using N2 physical adsorption, temperature-programmed reduction/ desorption (TPR/TPD) and Moessbauer effect spectroscopy (MES) methods. The characterization results indicated that the BET surface area increases with increasing Al2O3 content and passes through a maximum at the Al2O3/Fe ratio of 10/100 (weight basis). After the point, it decreases with further increase in Al2O3 content. The incorporation of Al2O3 binder was found to weaken the surface basicity and suppress the reduction and carburization of iron-based catalysts probably due to the strong K-Al2O3 and Fe-Al2O3 interactions. Furthermore, the H2 adsorption ability of the catalysts is enhanced with increasing Al2O3 content. The FTS performances of the catalysts were tested in a slurry-phase continuously stirred tank reactor (CSTR) under the reaction conditions of 260 ℃, 1.5 MPa, 1000 h-1 and molar ratio of H2/CO 0.67 for 200 h. The results showed that the addition of small amounts of Al2O3 affects the activity of iron-based catalysts to a little extent. However, with further increase of Al2O3 content, the FTS activity and water gas shift reaction (WGS) activity are decreased severely. The addition of appropriate Al2O3 do not affect the product selectivity, but the catalysts incorporated with large amounts of Al2O3 have higher selectivity for light hydrocarbons and lower selectivity for heavy hydrocarbons.

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Effect of Ni Loading and CexZr1-xO2 Promoter on Ni-Based SBA-15 Catalysts for Steam Reforming of Methane Huijun Wan;Xiujin Li;Shengfu Ji*;Bingyao Huang;Kai Wang;Chengyue Li 2007, 16(2): 139-147.  DOI: 摘要 ( 10308 )   PDF   A series of Ni/SBA-15 catalysts with Ni contents ranging from 5wt% to 20wt% as well as 10wt%Ni/10wt%CexZr1-xO2/SBA-15 (x=0, 0.5, 1) were prepared. The structures of the catalysts were characterized using XRD, TPR, TEM and BET techniques. The catalytic activities of the catalysts for steam reforming of methane were evaluated in a continuous flow microreactor. The results indicated that both the Ni/SBA-15 and the Ni/CexZr1-xO2/SBA-15 catalysts had good catalytic activities at atmospheric pressure. The 10wt%Ni/SBA-15 catalyst exhibited excellent stability at 800 ℃ for time on stream of 740 h. After the reaction, carbon deposits were not formed on the surface of the catalyst. There existed a regular hexagonal mesoporous structure in the Ni/SBA-15 and the Ni/CexZr1-xO2/SBA-15 catalysts. The nickel species and the CexZr1-xO2 component were all confined in the SBA-15 mesopores. The CexZr1-xO2 could promote dispersion of the nickel species in the Ni/CexZr1-xO2/SBA-15 catalysts.

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Effect of CeO2 and CaO Promoters on Ignition Performance for Partial Oxidation of Methane over Ni/MgO-Al2O3 Catalyst Yejun Qiu;Jixiang Chen*;Jiyan Zhang 2007, 16(2): 148-154.  DOI: 摘要 ( 10743 )   PDF   The effect of CeO2 and CaO promoters on the ignition performance over Ni/MgO-Al2O3 catalyst for the partial oxidation of methane (POM) to synthesis gas was investigated. It was found that the POM reaction could not be ignited over 1wt%Ni/MgO-Al2O3 catalyst without the promoters in the temperature range from 773 K to 1073 K. CeO2 and CaO promoters enhanced the ignition performance and the POM reactivity of 1wt%Ni/MgO-Al2O3 catalyst remarkably. Moreover, the improving effect became greater with the increase of the promoter content under the investigated reaction conditions. The modification effects of CeO2 and CaO promoters were closely related to the concentration and reducibility of the surface and bulk oxygen species.

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Application of Fe2O3/Al2O3 Composite Particles as Oxygen Carrier of Chemical Looping Combustion Fang He;*;Hua Wang;Yongnian Dai 2007, 16(2): 155-161.  DOI: 摘要 ( 8952 )   PDF   Chemical looping combustion (CLC) of carbonaceous compounds has been proposed, in the past decade, as an efficient method for CO2 capture without cost of extra energy penalties. The technique involves the use of a metal oxide as an oxygen carrier that transfers oxygen from combustion air to fuels. The combustion is carried out in a two-step process: in the fuel reactor, the fuel is oxidized by a metal oxide, and in the air reactor, the reduced metal is oxidized back to the original phase. The use of iron oxide as an oxygen carrier has been investigated in this article. Particles composed of 80 wt% Fe2O3, together with Al2O3 as binder, have been prepared by impregnation methods. X-ray diffraction (XRD) analysis reveals that Fe2O3 does not interact with the Al2O3 binder after multi-cycles. The reactivity of the oxygen carrier particles has been studied in twenty-cycle reduction-oxidation tests in a thermal gravimetrical analysis (TGA) reactor. The components in the outlet gas have been analyzed. It has been observed that about 85% of CH4 converted to CO2 and H2O during most of the reduction periods. The oxygen carrier has kept quite a high reactivity in the twenty-cycle reactions. In the first twenty reaction cycles, the reaction rates became slightly higher with the number of cyclic reactions increasing, which was confirmed by the scanning electron microscopy (SEM) test results. The SEM analysis revealed that the pore size inside the particle had been enlarged by the thermal stress during the reaction, which was favorable for diffusion of the gaseous reactants into the particles. The experimental results suggested that the Fe2O3/Al2O3 oxygen carrier was a promising candidate for a CLC system.

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Carbon Nanotubes Supported Pt-Ru-Ni as Methanol Electro-Oxidation Catalyst for Direct Methanol Fuel Cells Fei Ye*;Shengzhou Chen;Xinfa Dong;Weiming Lin;* 2007, 16(2): 162-166.  DOI: 摘要 ( 10784 )   PDF   Carbon nanotubes (CNTs) supported Pt-Ru and Pt-Ru-Ni catalysts were prepared by chemical reduction of metal precursors with sodium borohydride at room temperature. The crystallographic properties and composition of the catalysts were characterized by X-ray diffraction (XRD) and energy dispersive X-ray (EDX) analysis, and the catalytic activity and stability for methanol electro-oxidation were measured by electrochemical impedance spectroscopy (EIS), linear sweep voltammetries (LSV), and chronoamperometry (CA). The results show that the catalysts exhibit face-centered cubic (fcc) structure. The particle size of Pt-Ru-Ni/CNTs catalyst is about 4.8 nm. The catalytic activity and stability of the Pt-Ru-Ni/CNTs catalyst are higher than those of Pt-Ru/CNTs catalyst.

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Preferential Oxidation of CO in Excess Hydrogen over CuO-CeO2 Catalyst Prepared by Chelating Method Zhigang Liu;Renxian Zhou*;Xiaoming Zheng 2007, 16(2): 167-172.  DOI: 摘要 ( 8871 )   PDF   The CuO-CeO2 catalyst prepared by chelating method has a superior catalytic performance for the preferential oxidation of CO in rich hydrogen, compared with the CuO-CeO2 catalyst prepared by coprecipitation method. The CO conversions over these catalysts, at 120 ℃ and 120000 ml/(g·h) in the absence of CO2 and H2O, are 99.6% and 88.6%, respectively, and the selectivity of O2 over these catalysts is very close (i.e. 51.3% and 55.8%, respectively). The influence of certain factors such as hydrogen concentration, carbon monoxide concentration, H2O, O2/CO ratios, and space velocity on the catalytic performance of CuO-CeO2 catalyst prepared by chelating method is also studied. The results show that the addition of hydrogen and H2O has a negative effect on the catalytic performance of CuO-CeO2 catalyst, however, the variation of space velocity and the O2/CO ratio causes a comparatively slight influence.

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Photocatalytic Synthesis of Hydrocarbon Oxygenates from C2H6 and CO2 over Pd-MoO3/SiO2 Catalyst Xitao Wang*;Zhong He;Shunhe Zhong;Xiufen Xiao 2007, 16(2): 173-178.  DOI: 摘要 ( 10495 )   PDF   Pd-MoO3/SiO2 catalyst has been prepared using the method of incipient wetness impregnation. The photo absorbing behaviors and chemisorbing properties of the catalyst have been characterized by UV-vis spectra and TPD-MS experiments. The results indicated that metal Pd loaded on MoO3/SiO2 has a significant effect on the photo absorbing performance of MoO3/SiO2, and an obvious blue shift of the absorption edge is produced. Under UV irradiation, the chemisorption state of CO2 undergoes decomposing process to form CO at 481 K, and a two-site adsorption state of ethane can be formed at around 496 K. Photo-oxidation of ethane using carbon dioxide can mainly produce propanal, ethanol and acetaldehyde in the temperature range of 353.423 K. The presence of metal Pd improves the catalytic activity remarkably.

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Effect of Addition of Base on Ceria and Reactivity of CuO/CeO2 Catalysts for Low-Temperature CO Oxidation Xiucheng Zheng*;Xiaoli Zhang;Shuping Wang;Xiangyu Wang;Shihua Wu* 2007, 16(2): 179-185.  DOI: 摘要 ( 9275 )   PDF   In this work, we have reported the influence of the addition of base (KOH) on the physicochemical property of ceria synthesized by alcohothermal process, and the alcohothermal mechanism was also put forward. Furthermore, the prepared CeO2 was used as the support to prepare CuO/CeO2 catalysts via the wet impregnation method. The samples were characterized by N2 adsorption-desorption, X-ray powder diffraction (XRD), high resolution transmission electron microscopy (HRTEM), and temperatureprogrammed reduction by H2 (H2-TPR). The catalytic properties of the CuO/CeO2 catalysts for lowtemperature CO oxidation were studied using a microreactor-GC system. The crystal size of CeO2-A was much smaller than that of CeO2-B, and the corresponding copper oxide catalysts exhibited higher catalytic activity than that of the CeO2-B-supported catalysts under the same reaction conditions. The alcohothermal mechanism indicated that KOH plays a key role in determining the physicochemical and catalytic properties of ceria-based materials.

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Synthesis of Pharmaceutical Intermediates by Toluene Benzylation over Heteropoly Acids on Different Support V. V. Bokade;*;G. D. Yadav* 2007, 16(2): 186-192.  DOI: 摘要 ( 8359 )   PDF   Selective formation of pharmaceutical intermediates like diphenylmethane, dimethyldiphenylmethane, benzyl toluene and benzoic acid by liquid phase, toluene benzylation with benzyl chloride as a benzylating agent, was systematically studied over plane clay (K-10, montmorillonite), plane H-Beta, plane MFI structured titanosilicate (TS-1) and heteropoly acids [HPA, namely dodecatungstophosphoric acid [H3PO4·12WO3·xH2O] (TPA), dodeca-molybdo phosphoric acid ammonium salt hydrate [H12Mo12N3O40P+aq] (DMAA), sodium tungstate hydrated purified [Na12WO4·2H2O] (STH)] supported on clay, H-beta and TS-1. The 20%TPA/Clay, 30%TPA/H-Beta and 30%TPA/TS-1, were observed to be the best catalyst samples over plane clay, plane H-Beta and plane TS-1. The catalyst samples are compared with respect to benzyl chloride conversion and selectivities for diphenylmethane, dimethyl-diphenylmethane, benzyl toluene and benzoic acid. The reaction follows the pseudo-first order rate power law model. The apparent rate constants are calculated and compared with the reported ones.

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Mathematical Simulation and Design of Three-Phase Bubble Column Reactor for Direct Synthesis of Dimethyl Ether from Syngas Dianhua Liu;Xing Hua;Dingye Fang* 2007, 16(2): 193-199.  DOI: 摘要 ( 10301 )   PDF   A three-phase reactor mathematical model was set up to simulate and design a three-phase bubble column reactor for direct synthesis of dimethyl ether (DME) from syngas, considering both the influence of part inert carrier backmixing on transfer and the influence of catalyst grain sedimentation on reaction. On the basis of this model, the influences of the size and reaction conditions of a 100000 t/a DME reactor on capacity were investigated. The optimized size of the 10000 t/a DME synthesis reactor was proposed as follows: diameter 3.2 m, height 20 m, built-in 400 tube heat exchanger (φ38×2 mm), and inert heat carrier paraffin oil 68 t and catalyst 34.46 t. Reaction temperature and pressure were important factors influencing the reaction conversion for different size reactors. Under the condition of uniform catalyst concentration distribution, higher pressure and temperature were proposed to achieve a higher production capacity of DME. The best ratio of fresh syngas for DME synthesis was 2.04.

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Catalytic Oxidation of Dimethyl Ether to Hydrocarbons over SnO2/MgO and SnO2/CaO Catalysts Lin Yu*;Jieyu Xu;Ming Sun;Xuetao Wang 2007, 16(2): 200-203.  DOI: 摘要 ( 9697 )   PDF   A novel reverse microemulsion method was used to prepare SnO2/MgO and SnO2/CaO catalysts. It was found that both the catalysts were active for the reaction of catalytic oxidation of dimethyl ether (DME) in the temperature range of 275 to 300 ℃. SnO2/CaO catalyst exhibits much higher activity than SnO2/MgO. On SnO2/CaO catalyst, DME conversion of 21.8% was obtained at 300 ℃, while selectivities to methyl formate (MF) and dimethoxyethane (DMET) of 19.1% and 59.0% respectively were obtained at 275 ℃.

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Bench-Scale Testing of Zinc Ferrite Sorbent for Hot Gas Clean-up Meisheng Liang;*;Hongyan Xu;Kechang Xie 2007, 16(2): 204-209.  DOI: 摘要 ( 10970 )   PDF   Advanced integrated gasification combined cycle (IGCC) power generation systems require the development of high-temperature, regenerable desulfurization sorbents, which are capable of removing hydrogen sulfide from coal gasifier gas to very low levels. In this paper, zinc ferrites prepared by co-precipitation were identified as a novel coal gas desulfurization sorbent at high temperature. Preparation of zinc ferrite and effects of binders on pore volume, strength and desulfurization efficiency of zinc ferrite desulfurizer were studied. Moreover, the behavior of zinc ferrite sorbent during desulfurization and regeneration under the temperature range of 350-400 ℃ are investigated. Effects of binders on the pore volume, mechanical strength and desulfurization efficiency of zinc ferrite sorbents indicated that the addition of kaolinite to zinc ferrite desulfurizer seems to be superior to other binders under the experimental conditions.

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Aerobic Oxidation of Benzyl Alcohol Catalyzed by Cu-Mn Mixed Oxides and 2,2,6,6-Tetramethyl-piperidyl-1-oxyl Yanchun Guo;Junfeng Zhao;Jinxia Xu;Wei Wang;Fengshou Tian;Guanyu Yang*;Maoping Song* 2007, 16(2): 210-212.  DOI: 摘要 ( 6803 )   PDF   Heterogeneous Cu-Mn mixed oxides can mediate TEMPO-catalyzed selective oxidation of benzyl alcohol by molecular oxygen under neutral condition, and is recyclable. In the case of the molar ratio of Cu and Mn over 1, the highly-dispersed CuO inside the Cu-Mn mixed oxides is responsible for the good performances in catalytic oxidation.

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Storage-Reduction of NOx over Combined Catalysts of Pt/Ba/Al2O3-Mn/Ba/Al2O3: Carbon Monoxide as Reductant Sha Deng;Xuehui Li*;Jianhua Xiao;Furong Wang;Lefu Wang 2007, 16(2): 213-216.  DOI: 摘要 ( 6811 )   PDF   Storage-reduction of NOx by carbon monoxide was investigated over combined catalysts of Mn/Ba/Al2O3-Pt/Ba/Al2O3. Combination of Mn/Ba/Al2O3 and Pt/Ba/Al2O3 catalysts in different ways showed excellent NOx storage-reduction performance and the content of Pt could be reduced by 50%. Not only the addition of 5Mn/15Ba/Al2O3 to 1Pt/15Ba/Al2O3 could improve its storage ability, but also enhance the NOx conversion consequently. NOx conversion over the combined catalysts (the combined catalysts I and II) was increased under dynamic lean-rich burn conditions, the maximum NOx conversion increased from 69.4% to respectively 78.8% and 75.7% over two combined catalysts.