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2009, Vol. 18, No. 3　Online: 2009-05-30

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Intelligent reforming catalysts: Trace noble metal-doped Ni/Mg(Al)O derived from hydrotalcites (Special column of methane transformation, Review) Katsuomi Takehira* 2009, 18(3): 237-259.  DOI: 摘要 ( 8800 )   PDF   Trace amounts of noble metal-doped Ni/Mg(Al)O catalysts were prepared starting from Mg-Al hydrotalcites (HTs) and tested in daily start-up and shut-down (DSS) operation of steam reforming (SR) of methane or partial oxidation (PO) of propane. Although Ni/Mg(Al)O catalysts prepared from Mg(Ni)-Al HT exhibited high and stable activity in stationary SR, PO and dry reforming of methane and propane, the Ni/Mg(Al)O catalysts were drastically deactivated due to Ni oxidation by steam as purge gas when they were applied in DSS SR ofmethane. Such deactivation was effectively suppressed by doping trace amounts of noble metal on the catalysts by using a “memory effect” of HTs. Moreover, the noble metal-doped Ni/Mg(Al)O catalysts exhibited “intelligent” catalytic behaviors, i.e., self-activation and self-regenerative activity, leading to high and sustainable activity during DSS operation. Pt was the most effective among noble metals tested. The self-activation occurred by the reduction of Ni2+ in Mg(Ni,Al)O periclase to Ni0 assisted by hydrogen spillover from Pt (or Pt-Ni alloy). The self-regenerative activity was accomplished by self-redispersion of active Ni0 particles due to a reversible reductionoxidation movement of Ni between the outside and the inside of the Mg(Al)O periclase crystal; surface Ni0 was oxidized to Ni2+ by steam and incorporated into Mg(Ni2+,Al)O periclase, whereas the Ni2+ in the periclase was reduced to Ni0 by the hydrogen spillover and appeared as the fine Ni0 particles on the catalyst surface. Further a “green” preparation of the Pt/Ni/[Mg3.5Al]O catalysts was accomplished starting from commercial Mg3.5-Al HT by calcination, followed by sequential impregnation of Ni and Pt.

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Energy-Efficient coaromatization of methane and propane (Special column of methane transformation, Review) Jianjun Guo;Hui Lou;Xiaoming Zheng* 2009, 18(3): 260-272.  DOI: 摘要 ( 7557 )   PDF   Development of highly effective catalysts for one-stage conversion of methane with high selectivity to valuable products and energy efficiency will provide an efficient way to utilize natural gas and oil-associated gases and to protect environment. In recent years, there have been many efforts on direct catalytic transformations of methane into higher hydrocarbons by feeding additives together with methane under non-oxidative conditions. This paper reviewed the advances in recent research on non-oxidative aromatization of methane in the presence of propane over different modified HZSM-5 catalysts. The thermodynamic consideration, the isotope verification and the mechanism of the activation of methane in the presence of propane are discussed in the paper in detail.

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Kinetics of oxidative coupling of methane: bridging the gap between comprehension and description (Special column of methane transformation, Review) M. Yu. Sinev;Z. T. Fattakhova;V. I. Lomonosov;Yu. A. Gordienko 2009, 18(3): 273-287.  DOI: 摘要 ( 9115 )   PDF   The development of notions about the mechanism of the oxidative coupling of methane (OCM) over oxide catalysts and corresponding progress in its kinetic description are reviewed and discussed. The latter becomes essential at the stage of scaling up and optimization of the process in pilot and industrial reactors. It is demonstrated that the main achievements in the development of kinetic models can be reached by combining the approaches conventionally used in homogeneous gas-phase kinetics and in heterogeneous catalysis. In particular, some important features of the OCM process can be described if several elementary reactions of free radical species (formation and transformation) with surface active sites are included into the detailed scheme of methane oxidation in gas. However, some important features, such as a non-additive character of the reciprocal influence of methane and ethane in the case of their simultaneous presence in the reaction mixture, cannot yet be described and comprehended in the framework of schemes developed so far. Possible ways towards an advanced kinetic model, accounting the main principles of catalyst functioning (redox nature of active sites) and pathways of product formation (via free radicals) are traced.

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Selective oxidation of methane to formaldehyde by oxygen over silica-supported iron catalysts (Special column of methane transformation, Article) Jieli He;Yang Li;Dongli An;Qinghong Zhang;Ye Wang* 2009, 18(3): 288-294.  DOI: 摘要 ( 8776 )   PDF   FeOx-SiO2 catalysts prepared by a sol-gel method were studied for the selective oxidation of methane by oxygen. A single-pass formaldehyde yield of 2.0% was obtained over the FeOx-SiO2 with an iron content of 0.5 wt% at 898 K. This 0.5 wt% FeOx-SiO2 catalyst demonstrated significantly higher catalytic performances than the 0.5 wt% FeOx/SiO2 prepared by an impregnation method. The correlation between the catalytic performances and the characterizations with UV-Vis and H2-TPR suggested that the higher dispersion of iron species in the catalyst prepared by the sol-gel method was responsible for its higher catalytic activity for formaldehyde formation. The modification of the FeOx-SiO2 by phosphorus enhanced the formaldehyde selectivity, and a single-pass formaldehyde yield of 2.4% could be attained over a P-FeOx-SiO2 catalyst (P/Fe = 0.5) at 898 K. Raman spectroscopic measurements indicated the formation of FePO4 nanoclusters in this catalyst, which were more selective toward formaldehyde formation.

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Low temperature catalytic conversion of methane to formic acid by simple vanadium compound with use of H2O2 (Special column of methane transformation, Article) Xin Wei;Linmin Ye;Youzhu Yuan* 2009, 18(3): 295-299.  DOI: 摘要 ( 7575 )   PDF   Selective oxidation of methane with hydrogen peroxide was catalyzed by several simple vanadium compounds in CH3CN. The reaction could afford formic acid as the major product. Vanadyl oxysulfate (VOSO4) was found to be an efficient catalyst. Specifically, the selectivity to formic acid of 70% at a methane conversion of 6.5% could be achieved over the VOSO4 catalyst under the reaction conditions of methane pressure 3.0 MPa and temperature 333 K for 4 h. The UV-Vis spectroscopic measurements revealed that the formation of V5+ species during the reaction might be vital for the methane activation. The reaction probably proceeded via radical mechanism.

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Oscillations during partial oxidation of methane to synthesis gas over Ru/Al2O3 catalyst (Special column of methane transformation, Article) Meiliu Wang;Weizheng Weng*;Haozhuan Zheng;Xiaodong Yi;Chuanjing Huang;Huilin Wan* 2009, 18(3): 300-305.  DOI: 摘要 ( 8864 )   PDF   Oscillations in temperatures of catalyst bed as well as concentrations of gas phase species at the exit of reactor were observed during the partial oxidation of methane to synthesis gas over Ru/Al2O3 in the temperature range of 600 to 850 ◦C. XRD, H2-TPR and in situ Raman techniques was used to characterize the catalyst. Two types of ruthenium species, i.e. the ruthenium species weakly interacted with Al2O3 and that strongly interacted with the support, were identified by H2-TPR experiment. These species are responsible for two types of oscillation profiles observed during the reaction. The oscillations were the result of these ruthenium species switching cyclically between the oxidized state and the reduced state under the reaction condition. These cyclic transformations, in turn, were the result of temperature variations caused by the varying levels of the strongly exothermic CH4 combustion and the highly endothermic CH4 reforming (with H2O and CO2) reactions (or the less exothermic direct partial oxidation of methane to CO and H2), which were favored by the oxidized and the metallic sites, respectively. The major pathway of synthesis gas formation over the catalyst was via the combustion-reforming mechanism.

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Synthesis of dimethyl ether from methane mediated by HBr (Special column of methane transformation, Article) Qin You;Zhen Liu;Wensheng Li;Xiaoping Zhou;* 2009, 18(3): 306-311.  DOI: 摘要 ( 8451 )   PDF   Dimethyl ether (DME) was synthesized from methane through a two-step process, in which CH3Br was prepared from the oxidative bromination reaction of methane in the presence of HBr and oxygen over a Rh-SiO2 catalyst and then, in the second step, CH3Br was hydrolyzed to DME over a silica supported metal chloride catalyst. 12 mol%ZnCl2/SiO2 catalyst was found to be the most active, but it deactivated because of Cl− losing.

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Synthesis of self-assembled nanorod vanadium oxide bundles by sonochemical treatment Y. H. Taufiq-Yap;*;Y. C. Wong;Z. Zainal;M. Z. Hussein; 2009, 18(3): 312-318.  DOI: 摘要 ( 8489 )   PDF   Self-assembled nanorod of vanadium oxide bundles were synthesized by treating bulk V2O5 with high intensity sonochemical technique. The synthesized materials were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM) and temperature-programmed reduction (TPR) in H2. Catalytic behaviour of the materials over anaerobic n-butane oxidation was studied through temperature-programmed reaction (TPRn). Catalytic evaluation of the sonochemical treated V2O5 products was also studied on microreactor. XRD patterns of all the vanadium samples were perfectly indexed to V2O5. The morphologies of the nanorod vanadium oxides as shown in SEM and TEM depended on the duration of the ultrasound irradiation. Prolonging the ultrasound irradiation duration resulted in materials with uniform, well defined shapes and surface structures and smaller size of nanorod vanadium oxide bundles. H2-TPR profiles showed that larger amount of oxygen species were removed from the nanorod V2O5 compared to the bulk. Furthermore, the nanorod vanadium oxide bundles, which were produced after 90, 120 and 180 min of sonochemical treatment, showed an additional reduction peak at lower temperature (~850 K), suggesting the presence of some highly active oxygen species. TPRn in n-butane/He over these materials showed that the nanorod V2O5 with highly active oxygen species showed markedly higher activity than the bulk material, which was further proven by catalytic oxidation of n-butane.

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Oxidation of propane over substituted Keggin phosphomolybdate salts T. Mazari;C. Roch. Marchal;S. Hocine;N. Salhi;C. Rabia* 2009, 18(3): 319-324.  DOI: 摘要 ( 7985 )   PDF   Ammonium salts, (NH4)6HPMo11MO40 (M= Ni, Co, Fe), have been investigated for the oxidation of propane, with molecular oxygen, at temperature ranging between 380 ◦C and 420 ◦C after in-situ pre-treatment performed at two heating rate of 5 or 9 ◦C/min. They were characterized by BET method, XRD, 31P NMR, UV-Vis and IR techniques. The catalysts were found active in the propane oxidation and selective to propene or acrolein, in particular for samples pre-treated with the heating rate of 9 ◦C/min.

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Nanosized cobalt-based catalyst prepared by supercritical phase condition for Fischer-Tropsch synthesis Jingmiao Li;Jingchang Zhang*;Runduo Zhang;Weiliang Cao 2009, 18(3): 325-330.  DOI: 摘要 ( 10595 )   PDF   A series of nanosized Co/Zn/Mn/K composite catalysts for Fischer-Tropsch synthesis (FTS) were prepared by supercritical fluid dried (SCFD) method and common dried (CD) method. The nanosized cobalt-based catalysts were characterized by XRD, TEM and BET techniques. Their catalytic performances were tested in a slurry-bed reactor under FTS reaction conditions. The catalysts prepared by SCFD method have ideal structure and show the FTS performance superior to the others prepared by CD method. The drying and crystallization were carried out simultaneously during SCFD. The FTS activity and selectivity were improved via adding Zn, Mn and K promoters, and less CH4 and CO2 as well as higher yield of C5+ products were achieved. The optimal performance of a 92% CO conversion and a 65% C5+ product yield was obtained over catalyst with a component of Co/Zn/Mn/K = 100/50/10/7. Furthermore, the catalytic performance was studied under the conditions of liquid-phase and supercritical phase slurry-bed, and C5+ product yield were 57.4% and 65.4%, respectively. In summary, better catalytic performance was obtained using the nanosized catalyst prepared by SCFD method under supercritical reaction conditions, resulting in higher conversion of CO, less CO2 byproduct, and higher yield of C5+ products.

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Production of propene from 1-butene metathesis reaction on tungsten based heterogeneous catalysts Huijuan Liu;Ling Zhang;Xiujie Li;Shengjun Huang;Shenglin Liu;Wenjie Xin;Sujuan Xie;Longya Xu* 2009, 18(3): 331-336.  DOI: 摘要 ( 10735 )   PDF   A new propene production route from 1-butene metathesis has been developed on heterogeneous 10WO3/Al2O3-HY catalysts with different HY contents. It is found that the catalysts play bi-functionally first for the isomerization of 1-butene to 2-butene and then for the cross-metathesis between 1-butene and 2-butene to propene and 2-pentene. The combination of HY zeolite and Al2O3 is prerequisite for the production of propene. The propene yield keeps increasing with the HY content in the range of 10−70 wt%, where 10WO3/Al2O3-70HY exhibits the highest propene yield. The MS-H2-TPR and MS-O2-TPO characterizations indicate that the increase of HY content in the catalysts weakens the interaction between W species and supports, in contrast to the probability of coking on the metal species and acid sites.

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Conversion of syngas to higher alcohols over Cu-Fe-Zr catalysts induced by ethanol Hongtao Zhang;Xiaomei Yang;Lipeng Zhou;Yunlai Su;*;Zhongmin Liu 2009, 18(3): 337-340.  DOI: 摘要 ( 8316 )   PDF   Ethanol induced method was applied to prepare Cu-Fe-Zr catalysts for conversion of syngas to higher alcohols. The catalytic performance of the catalysts induced by ethanol was superior to that of the catalyst prepared by the conventional precipitation method. Among various procedures for ethanol induced method, it was found that incorporation of ethanol in the precipitation process was the better. After incorporation of ethanol, the crystal size of CuO decreased and the reduction of copper species became easier. The better activity of Cu-Fe-Zr catalysts prepared by ethanol induced procedures was probably caused by the higher dispersion of Cu species.

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Solvent effects on Pt-Ru/C catalyst for methanol electro-oxidation Jinwei Chen;Chunping Jiang;Hui Lu;Lan Feng;Xin Yang;Liangqiong Li;Ruilin Wang* 2009, 18(3): 341-345.  DOI: 摘要 ( 10935 )   PDF   Alloying degree, particle size and the level of dispersion are the key structural parameters of Pt-Ru/C catalyst in fuel cells. Solvent(s) used in the preparation process can affect the particle size and alloying degree of the object substance, which lead to a great positive impact on its properties. In this work, three types of the solvents and their mixtures were used in preparation of the Pt-Ru/C catalysts by chemical reduction of metal precursors with sodium borohydride at room temperature. The structure of the catalysts was characterized by X-ray diffraction (XRD) and Transmission electron microscopy (TEM). The catalytic activity and stability for methanol electro-oxidation were studied by Cyclic Voltammetry (CV) and Chronoamperometry (CA). Pt-Ru/C catalyst prepared in H2O or binary solvents of H2O and isopropanol had large particle size and low alloying degree leading to low catalytic activity and less stability in methanol electro-oxidation. When tetrahydrofuran was added to the above solvent systems, Pt-Ru/C catalyst prepared had smaller particle size and higher alloying degree which resulted in better catalytic activity, lower onset and peak potentials, compared with the above catalysts. Moreover, the catalyst prepared in ternary solvents of isopropanol, water and tetrahydrofuran had the smallest particle size, and the high alloying degree and the dispersion kept unchanged. Therefore, this kind of catalyst showed the highest catalytic activity and good stability for methanol electro-oxidation.

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High performance CuO-CeO2 catalysts for selective oxidation of CO in excess hydrogen: Effect of hydrothermal preparation conditions Pengfei Zhu;Jing Li;Qinqin Huang;Siming Yan;Mei Liu;Renxian Zhou* 2009, 18(3): 346-353.  DOI: 摘要 ( 10494 )   PDF   High performance CuO-CeO2 catalysts for selective oxidation of CO in excess hydrogen were prepared by a hydrothermal method under different preparation conditions and evaluated for catalytic activities and selectivities. By changing the nCTAB/nCe ratio and hydrothermal aging time, the catalytic activity of the CuO-CeO2 catalysts increased and the operating temperature window, in which the CO conversion was higher than 99%, was widened. XRD results showed no peaks of CuOx or peaks of Cu-Ce-O solid solution were observed. On the other hand, Cu+ species in the CuO-CeO2 catalysts, which was associated with a strong interaction between copper oxide clusters and cerium oxide and could be favorable for improving the selective oxidation performance of CO in excess H2, were detected by H2-TPR and XPS techniques.

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Effects of promoters on catalytic performance of Fe-Co/SiO2 catalyst for Fischer-Tropsch synthesis Xiangdong Ma;Qiwen Sun;Weiyong Ying*;Dingye Fang 2009, 18(3): 354-358.  DOI: 摘要 ( 8775 )   PDF   2%Fe10%Co/SiO2 catalysts with different potassium or zirconium loadings were prepared by aqueous incipient wetness impregnation and tested in Fischer-Tropsch synthesis in a flow reactor, using H2/CO = 1.6 (molar ratio) in the feed, under the condition of an overall pressure of 1 MPa, GHSV of 600 h−1 and temperature of 503 K. The zirconium and potassium promoters remarkably influenced hydrocarbon distribution of the products. CO conversion increased on the catalysts with the increase of zirconium loadings, which indicated that zirconium enhanced the activity of iron-cobalt catalysts. Low potassium loadings also enhanced the activity of the catalysts. However, high potassium loading made CO conversion on the catalysts decrease and weakened the secondary hydrogenations. The characterizations of catalysts were obtained by BET, XRD and TPR. The fresh catalysts revealed the presence of a Co3O4 phase, and the spinel phase of Fe-Co alloy and CoO was formed on the used catalysts.

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Deep oxidation in propane oxidative dehydrogenation to propene over V2O5/-Al2O3 studied by in-situ DRIFTS Yunbing He;Hongbing Ji*;Jianhua Xu;Lefu Wang 2009, 18(3): 359-364.  DOI: 摘要 ( 8098 )   PDF   In-situ DRIFTS was used to study the deep oxidation of propane, a side reaction during propane oxidative dehydrogenation to propene. Strong adsorption of propene was supposed to be the main reason for the deep oxidation. It was found that gaseous oxygen in the feed and the reaction temperature had great influence on the reaction. To obtain a relative high selectivity to propene, the reaction temperature should be maintained at 150-250 ◦C with a proper content of gaseous oxygen in the feed for a certain catalyst and some modifiers which could weaken the adsorption of propene on the catalyst surface would be favorable.

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Preparation of a kind of mesoporous carbon and its performance in adsorptive desulfurization Haiyun Zhou;Gang Li*;Xiaoxing Wang;Changzi Jin;Yongying Chen 2009, 18(3): 365-368.  DOI: 摘要 ( 7859 )   PDF   Carbon materials were prepared using mesoporous silica HMS with different pore sizes as the hard templates and water-soluble phenolic resin as the carbon source. The obtained materials were characterized by powder X-ray diffraction, transmission electron microscopy and N2 physical adsorption, and were used in adsorptive desulfurization. It has been shown that the carbon material prepared using HMS with larger pore size (>3 nm) presented uniform wormlike mesopore of 2.3 nm and large BET surface area (1903 m2/g). The mesoporous carbon was an excellent adsorbent to remove the refractory sulfur compound in diesel, especially dibenzothiophene and 4, 6-dimethyldibenzothiophene.

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Disproportionation of ethylbenzene in the presence of C8 aromatics N. Sharnappa;S. Pai;V. V. Bokade 2009, 18(3): 369-374.  DOI: 摘要 ( 7380 )   PDF   The selective synthesis of p-diethylbenzene (p-DEB) by disproportionation of ethylbenzene (EB) in the presence of aromatics like m- and pxylene isomers has been studied over a pore size regulated HZSM-5 catalyst. The industrial feed having different compositions of ethylbenzene and xylene isomers was used for the experimentation. Hence, they were expected to hinder the movement of reactant molecules both on the external surface and within the zeolite channels. It was observed that irrespective of the different feed compositions the concentration of the xylene isomers was intact in the product. There is no other byproducts formation like para-ethylmethyl benzene. The effects of varying the concentration of aromatic compounds in the feed on ethylbenzene conversion and product distribution over the parent and modified H-ZSM-5 catalyst have been discussed. Ethylebenzene disproportionation reaction follows the pseudo first order reaction with an activation energy of 8.6 kcal/mol.

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Promoting effect of polyoxyethylene octylphenol ether on Cu/ZnO catalysts for low-temperature methanol synthesis Ling Liu;Tiansheng Zhao*;Qingxiang Ma;Yufang Shen 2009, 18(3): 375-378.  DOI: 摘要 ( 8438 )   PDF   Cu/ZnO catalysts were prepared by the co-precipitation method with the addition of OP-10 (polyoxyethylene octylphenol ether) and were structurally characterized by means of XRD, BET, H2-TPR, CO-TPD and N2O-titration. The effect of OP-10 addition on the activity of Cu/ZnO for the slurry phase methanol synthesis at 150 ◦C was evaluated. Results showed that Cu/ZnO prepared with addition of 8% OP-10 (denoted as C8) exhibited the promoted activity for the methanol synthesis. The conversion of CO and the STY (space time yield) of methanol were 42.5% and 74.6% higher than those of Cu/ZnO prepared without addition of OP-10 (denoted as C0), respectively. The precursor of C8 contained more aurichalcite and rosasite, and the concerted effect of Cu-Zn in C8 was found to be stronger than that in C0. Compared with C0, C8 showed smaller particle size, lower reduction temperature and larger BET and Cu surface areas.

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Complete oxidation of ethanol over vanadium based catalysts Zhe Li*;Xia An;Panjie Ren;Wei Huang;Kechang Xie 2009, 18(3): 379-382.  DOI: 摘要 ( 8096 )   PDF   V2O5/γ-Al2O3-TiO2 catalysts were prepared by the mixing sol-gel and co-impregnation method. The performance of the catalysts for complete oxidation of ethanol was performed in a conventional fixed-bed quartz reactor. And the effects of support, preparation methods and vanadium content have been investigated. The results showed that 5% V2O5 catalyst supported on γ-Al2O3-TiO2 possessed the best ethanol conversion under the considered temperature. This may be ascribed to the highly dispersible active component, mutual function between the active component and the carriers. The nature of the best performance for 5%V/γ-Al2O3-TiO2 catalyst may be related to the high V4+ amounts on the surface. And the surface V4+ species may play an important role in the formation of active site for the total ethanol oxidation.