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2011, Vol. 20, No. 3　Online: 2011-05-20

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Conversion of carbon dioxide to valuable petrochemicals: An approach to clean development mechanism Farnaz Tahriri Zangeneh, Saeed Sahebdelfar, Maryam Takht Ravanchi* 2011, 20(3): 219-231.  DOI: 10.1016/S1003-9953(10)60191-0 摘要 ( 12194 )   The increase of atmospheric carbon dioxide and the global warming due to its greenhouse effect resulted in worldwide concerns. On the other hand, carbon dioxide might be considered as a valuable and renewable carbon source. One approach to reduce carbon dioxide emissions could be its capture and recycle via transformation into chemicals using the technologies in C1 chemistry. Despite its great interest, there are difficulties in CO2 separation on the one hand, and thermodynamic stability of carbon dioxide molecule rendering its chemical activity low on the other hand. Carbon dioxide has been already used in petrochemical industries for production of limited chemicals such as urea. The utilization of carbon dioxide does not necessarily involve development of new processes, and in certain processes such as methanol synthesis and methane steam reforming, addition of CO2 into the feed results in its utilization and increases carbon efficiency. In other cases, modifications in catalyst and/or processes, or even new catalysts and processes, are necessary. In either case, catalysis plays a crucial role in carbon dioxide conversion and effective catalysts are required for commercial realization of the related processes. Technologies for CO2 utilization are emerging after many years of research and development efforts.

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Relationship between the reducibility and selectivity of CeMoxV1-xO4 catalysts by kinetic parameters of TPR Bao Agula, Tiezhen Ren, Xu Zhao, Bao Zhaorigetu, Zhongyong Yuan* 2011, 20(3): 232-236.  DOI: 10.1016/S1003-9953(10)60182-X 摘要 ( 14275 )   CeVO4, CeMo0.01V0.99O4 and CeMo0.03V0.97O4 were prepared by co-precipitation method. The addition of molybdenum as promoter shows a positive effect on the catalytic behavior of CeVO4 in oxidative dehydrogenation of propane to propylene. The reduction behaviors of the catalysts were characterized by temperature-programmed reduction. The activation energies of reduction process for the catalysts were obtained at different reduction rates by Kissinger method. The addition of Mo to CeVO4 enhances the selectivity to propylene.

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Preparation of hierarchical mesoporous Zn/HZSM-5 catalyst and its application in MTG reaction Youming Ni, Aiming Sun, Xiaoling Wu, Guoliang Hai, Jianglin Hu, Tao Li*, Guangxi 2011, 20(3): 237-242.  DOI: 10.1016/S1003-9953(10)60184-3 摘要 ( 11651 )   The hierarchical mesoporous Zn/ZSM-5 zeolite catalyst was prepared by NaOH treatment and Zn impregnation, and its application in the conversion of methanol to gasoline (MTG) was studied. N2 adsorption-desorption results showed that the mesopores with sizes of 2--20 nm in HZ5/0.3AT was formed by 0.3 M NaOH alkali treatment. The zeolite samples after modification were also characterized by XRF, AAS, XRD, SEM and NH3-TPD methods. Zn impregnated catalyst Zn/HZ5/0.3AT exhibited dramatic improvements in catalytic lifetime and liquid hydrocarbons yield. The selectivity of aromatic hydrocarbons was also improved after Zn impregnation. It is suggested that the mesopores of Zn/HZ5/0.3AT enhanced the synergetic effect of Zn species and acid sites and the capability to coke tolerance, which were confirmed by the results of catalytic test and TGA analysis, respectively.

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Low-temperature activation of methane over rare earth metals promoted Zn/HZSM-5 zeolite catalysts in the presence of ethylene Hengqiang Zhang, Aiguo Kong, Yongjie Ding, Chengyong Dai, Yongkui Shan* 2011, 20(3): 243-248.  DOI: 10.1016/S1003-9953(10)60181-8 摘要 ( 12103 )   At low temperature of 723 K, methane can be easily activated in the presence of ethylene in the feed, and converted to higher hydrocarbons (C2--C4) and aromatics (C6--C10), through its reaction over rare metals modified Zn/HZSM-5 zeolite catalysts without undesirable carbon oxides formation. Methane can get 37.3% conversion over the above catalysts under low temperature, and the catalysts show a longer lifetime than usual metal supported HZSM-5 zeolite catalysts without adding any rare earth metals. The effects of methane activation over various rare earth metal promoted Zn/HZSM-5 catalysts on the products and influences of several reaction conditions such as temperature, catalyst lifetime and molar ratio of CH4/C2H4 have been discussed.

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Synergetic effect of TeMo5O16 and MoO3 phases in MoTeOx catalysts used for the partial oxidation of propylene Yiming He*, Ying Wu, Weizheng Weng, Huilin Wan* 2011, 20(3): 249-255.  DOI: 10.1016/S1003-9953(10)60194-6 摘要 ( 10241 )   A detailed study on the synergetic effect of TeMo5O16 and MoO3 phases in the MoTeOx catalysts for the partial oxidation of propylene to acrolein has been reported in this work. It was found that both propylene conversion and acrolein selectivity increased with the addition of MoO3 to TeMo5O16. Based on the results of N2 adsorption-desorption, XRD, XPS, in-situ XRD, O2-TPO, and 2-propanol decomposition reaction, the higher catalytic performance and synergetic effect could be attributed to the enhancement of acidity and the oxygen transfer from TeMo5O16 to MoO3 phase.

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The study on the dynamic response performance of PEMFC with electrodeposited RuO2•xH2O-Pt/C electrode Yanbo Wu, Xiaoxin Wu, Hongfeng Xu*, Lu Lu 2011, 20(3): 256-260.  DOI: 10.1016/S1003-9953(10)60190-9 摘要 ( 8953 )   Dynamic response performance of proton exchange membrane (PEM) fuel cells affects its durability and reliability significantly. In this study, electrodeposited RuO2•xH2O-Pt/C was prepared to promote the PEM fuel cell dynamic response performance. The prepared RuO2•xH2O-Pt/C was characterized by scanning electron microscopy (SEM) equipped with energy disperse spectroscopy (EDS), which shows RuO2•xH2O was electrodeposited on the surface of Pt/C. Performance of single cells with and without RuO2•xH2O-Pt/C at the cathode under a certain operating condition was studied using cyclic voltammetry, electrochemical impedance spectra (EIS) and polarization curve techniques. When the fuel cell modified with RuO2•xH2O-Pt/C was operated at lower pressure, a faster and more stable dynamic response could be found. Modifying with RuO2•xH2O-Pt/C composite material not only slightly increases the single cell performance but also dramatically improves the dynamic response performance, which revealing that RuO2•xH2O-Pt/C can buffer the voltage undershoot whenever the current increases instantly.

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Effects of ammonium exchange and Si/Al ratio on the conversion of methanol to propylene over a novel and large partical size ZSM-5 Ruchao Wei, Chunyi Li*, Chaohe Yang, Honghong Shan 2011, 20(3): 261-265.  DOI: 10.1016/S1003-9953(10)60198-3 摘要 ( 11821 )   One type of ZSM-5 zeolite with large partical size was prepared and characterized by XRD, SEM, N2 adsorption-desorption, XRF, Py-IR and NH3-TPD techniques. Effects of ammonium exchange and SiO2/Al2O3 molar ratios on the reaction of methanol to propylene (MTP) over Na-ZSM-5 and H-ZSM-5 zeolites have been studied in a fixed-bed flow reactor under the operating conditions of T = 500 ℃, P = 1 atm, and WHSV = 6 h-1. Ammonium exchange led to a rapid decrease in Na content for Na-ZSM-5 zeolite. The reaction results indicated that Na-ZSM-5 and H-ZSM-5 with different SiO2/Al2O3 molar ratios all exhibited high activity for methanol conversion. Ammonium exchange and the decreased SiO2/Al2O3 molar ratio of ZSM-5 zeolite led to an increase both in strong acid sites and weak acid sites. Na-ZSM-5 with high SiO2/Al2O3 molar ratio was favorable for the formation of propylene. The highest propylene selectivity (45.9%) was obtained over Na-ZSM-5 zeolite catalyst with SiO2/Al2O3 molar ratio of 220.

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Study on the deactivation and regeneration of the ZSM-5 catalyst used in methanol to olefins Jingchang Zhang*, Haibin Zhang, Xiuying Yang, Zhong Huang, Weiliang Cao 2011, 20(3): 266-270.  DOI: 10.1016/S1003-9953(10)60183-1 摘要 ( 13199 )   ZSM-5 zeolite catalyst modified by a trace of metal cations shows high activity and high selectivity for the reaction of methanol to olefins (MTO), but it inclines to deactivate during the reaction. In this paper, the mechanism of the catalyst deactivation and the regeneration method were studied by X-ray diffraction (XRD), N2 adsorption-desorption, infrared spectra (IR), and infrared spectra coupled with NH3 molecular probes (IR-NH3). These characterizations indicated that coke formation was the main reason for the catalyst deactivation. To regenerate the deactivated catalyst, two methods, i.e., calcination and methanol leaching, were used. N2 adsorption-desorption, IR and IR-NH3 characterizations showed that both methods can eliminate coke deposited on the catalyst and make the catalyst reactivated. XRD showed that the structure of the catalyst did not change after regeneration. Interestingly, the regenerated catalyst even showed better catalytic performance of the MTO reaction than the fresh one. Besides, the calcination regeneration can eliminate coke more completely, however, the methanol leaching method can be more easily carried out in situ in the reactor.

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Single-step thermal carburization synthesis of supported molybdenum carbides from molybdenum-containing methyl-silica Juan Zou*, Minglin Xiang, Bo Hou, Dong Wu, Yuhan Sun 2011, 20(3): 271-280.  DOI: 10.1016/S1003-9953(10)60178-8 摘要 ( 12628 )   A novel synthesis route to obtain highly dispersed molybdenum carbides in porous silica is described. The synthesis was carried out by a single-step heat treatment of molybdenum-containing and methyl-modified silica (Mo-M-SiO2) in argon atmosphere at 973 K. Mo-M-SiO2 precursor was facilely obtained via a one-pot synthesis route, using (NH4)6Mo7O24•4H2O (AHM) as molybdenum sources and polymethylhydrosiloxane (PMHS) as silica sources at the initial synthetic step. The optimal C/Mo molar ratio in reaction system for complete carburization of molybdenum species was 7. The carburization process of molybdenum species followed a nontopotactic route involving a MoO2 intermediate phase, which was evidenced by XRD, N2 adsorption-desorption and in situ XPS. Formation mechanism of Mo-M-SiO2 precursor was also proposed by observation of the reaction between AHM and PMHS with TEM. Furthermore, by adding TEOS into silica sources and adjusting TEOS/PMHS mass ratio, crystal phase of molybdenum carbides transferred from β-Mo2C to α-MoC1-x, and SiO2 structure changed from microporous to micro/mesoporous. Catalytic performances of samples were tested using CO hydrogenation as a probe reaction. The supported molybdenum carbides exhibited high selectivity for higher alcohol synthesis compared with bulk β-Mo2C and α-MoC1-x.

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Hydrogen and syngas production from two-step steam reforming of methane using CeO2 as oxygen carrier Xing Zhu, Hua Wang*, Yonggang Wei, Kongzhai Li, Xianming Cheng 2011, 20(3): 281-286.  DOI: 10.1016/S1003-9953(10)60185-5 摘要 ( 12956 )   CeO2 oxygen carrier was prepared by precipitation method and tested by two-step steam reforming of methane (SRM). Two-step SRM for hydrogen and syngas generation is investigated in a fixed-bed reactor. Methane is directly converted to syngas at a H2/CO ratio close to 2 : 1 at a high temperature (above 750 ℃) by the lattice oxygen of CeO2; methane cracking is found when the reduction degree of CeO2 was above 5.0% at 850 ℃ in methane isothermal reaction. CeO2-δ obtained from methane isothermal reaction can split water to generate CO-free hydrogen and renew its lattice oxygen at 700 ℃; simultaneously, deposited carbon is selectively oxidized to CO2 by steam following the reaction (C+2H2O→CO2+2H2). Slight deactivation in terms of amounts of desired products (syngas and hydrogen) is observed in ten repetitive two-step SRM process due to the carbon deposition on CeO2 surface as well as sintering of CeO2.

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Hydrogen production through diesel steam reforming over rare-earth promoted Ni/γ-Al2O3 catalysts Lihao Xu, Wanliang Mi, Qingquan Su* 2011, 20(3): 287-293.  DOI: 10.1016/S1003-9953(10)60188-0 摘要 ( 11177 )   Rare-earth (La, Ce, Yb) promoted Ni/γ-Al2O3 catalysts were prepared by impregnation method. Activity and carbon formation resistance of the prepared catalysts were evaluated under various reaction conditions. Catalyst characterizations with TG, TPR and H2 chemisorption were carried out to investigate the promoting mechanism. Experimental results show that rare-earth promoters, especially Yb promoter, obviously improve the activity and carbon formation resistance of Ni/γ-Al2O3 catalyst, and Yb-Ni catalyst shows even higher performance than several commercial catalysts. According to the characterization results, Yb promoter enhances the interaction between the active metal and support, thus increasing the active metal's dispersion and improving its performance. Furthermore, the obvious difference in diesel conversion between Yb-Ni catalyst and others was shown in the temperature range of 450-550 ℃, which would be the reason for its excellent carbon resistance.

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A novel solid-gas process to synthesize LaMnO3 perovskite with high surface area and excellent activity for methane combustion Guojun Zou, Zhonglai Wang, Mingjuan Sun, Xu Luo, Xiaolai Wang* 2011, 20(3): 294-298.  DOI: 10.1016/S1003-9953(10)60186-7 摘要 ( 11486 )    A novel solid-gas route to prepare LaMnO3 perovskite catalysts for methane combustion has been developed. The method was carried out using a polyvinylpyrrolidone-metal complex as precursor via a solid-gas process to obtain the target materials. The structure and properties of the precursor and the catalysts were characterized by FT-IR, TG-DSC, XRD and N2 adsorption-desorption techniques. The results indicate that the catalysts synthesized via the solid-gas process possess higher surface areas, better thermal resistance and catalytic activity as compared to those prepared with the conventional sol-gel citrate method.

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Catalysts derived from waste slag for transesterification Xiaowei Zhang, Wei Huang* 2011, 20(3): 299-302.  DOI: 10.1016/S1003-9953(10)60189-2 摘要 ( 11700 )   MgO-CaO/SiO2 solid catalysts derived from waste slag (WS) of metal magnesium plant were prepared. The catalytic performances were evaluated in the transesterification of rapeseed oil with methanol to biodiesel in a 500 mL three-necked reactor under atmospheric pressure. The basic strengh of the catalyst reached 22.0 measured by indicators accroding to Hammett scale. The results show that the MgO-CaO/SiO2 is an excellent catalyst for transesterification, and the conversion of rapeseed oil reach 98% under the optimum condition.

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Metal catalyzed ethylene epoxidation: A comparative density functional theory study Ruipeng Ren, Yongkang Lü*, Xianyong Pang, Guichang Wang* 2011, 20(3): 303-310.  DOI: 10.1016/S1003-9953(10)60176-4 摘要 ( 10309 )   Ethylene epoxidation on Ag(111), Pt(111), Rh(111) and Mo(100) has been studied by density functional theory (DFT) calculations. The results show that the adsorption energies of possible adsorbed species involved in the ethylene epoxidation increase in the order: Ag<Pt<Rh<Mo, and the activation energies of the formation of epoxide (EtO) and acetaldehyde (Ac) follow the same order. Moreover, it is found that the smallest difference in the activation energies between EtO formation and Ac formation is shown on Ag. These results indicate that the metallic Ag shows the highest between activity and selectivity for ethylene epoxidation among the studied metal surfaces. Perhaps, the stability of OMME intermediate is the crucial factor in controlling the activity and selectivity. And the stronger the binding of OMME, the lower the activity and selectivity are. In addition, the relationships between the reaction enthalpy and activation energy on these four metal surfaces are investigated, and it is found that such a correlation is only applied for OMME(a)→ EtO(a) and OMME(a) →Ac(a), while invalid for the case of C2H4(a) + O(a)→ OMME(a).

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Intrinsic kinetics of oxidative dehydrogenation of propane in the presence of CO2 over Cr/MSU-1 catalyst Haitao Liu, Zhao Zhang, Huiquan Li*, Qingze Huang 2011, 20(3): 311-317.  DOI: 10.1016/S1003-9953(10)60180-6 摘要 ( 13885 )   The intrinsic kinetics of oxidative dehydrogenation of propane with CO2 has been investigated over Cr/MSU-1 catalyst in a fixed bed reactor. Without limitations of both internal and external diffusion, intrinsic kinetic data were obtained under the following conditions: 490-530 ℃, space velocity of 3600-6000 mL·h-1·g-1 and 3/1 molar ratio for CO2/C3H8 under normal pressure. Based on Langmuir-Hinshelwood mechanism, the kinetic models were established, and they were validated by statistical analysis. The parameters were estimated using Simplex Method combined with Universal Global Optimization Algorithm. The model, taking the surface reaction process as the rate-determining step, is the best one in agreement with the experimental data.

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Methanation of carbon dioxide on Ni/ZrO2-Al2O3 catalysts: Effects of ZrO2 promoter and preparation method of novel ZrO2-Al2O3 carrier Mengdie Cai, Jie Wen*, Wei Chu, Xueqing Cheng, Zejun Li 2011, 20(3): 318-324.  DOI: 10.1016/S1003-9953(10)60187-9 摘要 ( 14284 )   The novel nickel-based catalysts with a nickel content of 12 wt% were prepared with the zirconia-alumina composite as the supports. The new carriers, ZrO2 improved alumina, were synthesized by three methods, i.e., impregnation-precipitation, co-precipitation, and impregnation method. The catalytic properties of these catalysts were investigated in the methanation of carbon dioxide, and the samples were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscope (XPS), temperature-programmed reduction (TPR) and temperature-programmed desorption (TPD) techniques. The new catalysts showed higher catalytical activity and better stability than Ni/γ-Al2O3. Furthermore, as a support for new nickel catalyst, the ZrO2-Al2O3 composite prepared by the impregnation-precipitation method was more efficient than the other supports in the methanation of carbon dioxide. The highly dispersed zirconium oxide on the surface of γ-Al2O3 inhibited the formation of nickel aluminate-like phase, which was responsible for the better dispersion of Ni species and easier reduction of NiO species, leading to the enhanced catalytic performance of corresponding catalyst.

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A simple kinetic model for oxidative coupling of methane over La0.6Sr0.4Co0.8Fe0.2O3-δ nanocatalyst Ali Farsi*, Sattar Ghader, Ali Moradi, Seyed Soheil Mansouri, Vahid Shad 2011, 20(3): 325-333.  DOI: 10.1016/S1003-9953(10)60179-X 摘要 ( 11618 )   A simplified kinetic model for the oxidative coupling of methane over a La0.6Sr0.4Co0.8Fe0.2O3-δ nanocatalyst is presented. The kinetic model was developed by experimental data in a catalytic micro-reactor covering a wide range of reaction conditions (0.04<PO2<0.15 atm, 0.2<PCH4<0.85 atm, 800<T<900 ℃). Power law rate expressions were used for all reactions. The reaction scheme proposed in this work includes the most important reactions of oxidative coupling of methane and those involved in most of the available mechanisms in the literature. From the experimental data, kinetic parameters, i.e., pre-exponential factors, activation energies and power law exponents, were estimated. The compatibility of model results with experimental data was investigated and the accuracy of the model prediction was evaluated. Rates of methane consumption, C2+ and COx formation, methane conversion, and C2+ selectivity and yield were compared with experimental data using presented kinetics. The kinetic model was also compared with four previous kinetic models in terms of methane conversion.

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Preparation of nanocrystalline γ-Al2O3 catalyst using different procedures for methanol dehydration to dimethyl ether Ahmad Reza Keshavarz, Mehran Rezaei*, Fereydoon Yaripour 2011, 20(3): 334-338.  DOI: 10.1016/S1003-9953(10)60157-0 摘要 ( 13077 )   A series of nanocrystalline γ-alumina are synthesized by different procedures, namely, thermal decomposition method (sample A), precipitation method (sample B) and sol-gel method using sucrose and hexadecyltrimethyl ammonium bromide (CTAB) as templates (samples C and D, respectively). Textural and acidic properties of γ-alumina samples are characterized by XRD, N2 adsorption-desorption and NH3-TPD techniques. Vapor-phase dehydration of methanol into dimethyl ether is carried out over these samples. Among them, sample C shows the highest catalytic activity. NH3-TPD analysis reveals that the sample with smaller crystallite size possesses higher concentration of medium acidic sites and consequently higher catalytic activity. Thermal decomposition method leads to decrease in both surface area and moderate acidity, therefore it is the cause of lower catalytic activity.