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2008, Vol. 17, No. 3　Online: 2008-09-30

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Preparation of La-Mo-V mixed-oxide systems and their application in the direct synthesis of acetic acid Hamid Reza Arandiyan;Matin Parvari* 2008, 17(3): 213-224.  DOI: 摘要 ( 9953 )   PDF   In this study, mixed metal oxides developed with a perovskite-type structure that show great potential for use in catalysis. Perovskite oxide catalysts with the composition LaMoxV1-xOn (x = 0.1, 0.3, 0.5, 0.7, and 0.9) have been synthesized by the sol-gel method and then used in the ethane dry reforming reaction for the direct synthesis of acetic acid. The influence of the nature of the metallic source (metal, nitrate, acetylacetonate, and ammonium) on gel formation has been studied by Fourier-transform infrared spectroscopy (FT-IR) and thermogravimetric analysis (TGA-DTA). After calcination, the obtained perovskites were characterized by X-ray diffraction (XRD) and energy-dispersive X-ray spectrometry (EDS) coupled with scanning electron microscopy (SEM). The catalysts were then subjected to thermo-programmed reduction (TPR). The surface area (BET) was found to increase from 2.6 m2/g (x = 0.1) to 5.1 m2/g (x = 1.0) with increasing molybdenum content following calcinations at 750 oC, and pure LaMoxV1-xOn perovskite was obtained with good homogeneity. The catalysts have been characterized by XRD, SEM, EDS, and carbon analysis (CA). The results indicate that through this synthesis it is possible to obtain highly crystalline, homogeneous and pure solids, with well-defined structures. The direct synthesis of acetic acid from ethane over the perovskite catalysts was studied at temperatures between 450 and 850 oC and elevated pressures between 1 and 8 bar. It was found that the yield of acetic acid and the selectivity of its formation could be increased by incorporating more molybdenum into the perovskite structure. The experimental studies have shown that the calcination temperature and the molybdenum content have a significant influence on the catalytic activity. Amongst the catalysts tested, LaMo0.7V0.3O4.2 exhibited the best activity and stability.

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Effect of MgO promoter on Ni-based SBA-15 catalysts for combined steam and carbon dioxide reforming of methane Bingyao Huang;Xiujin Li;Shengfu Ji*;Bao Lang;Fabien Habimana;Chengyue Li 2008, 17(3): 225-231.  DOI: 摘要 ( 11436 )   PDF   A series of Ni/SBA-15 catalysts with Ni contents ranging from 5 wt% to 15 wt%, as well as another series of 10%Ni/MgO/SBA-15 catalysts, in which the range of the MgO content was from 1 wt% to 7 wt%, were prepared, and their catalytic performances for the reaction of combined steam and carbon dioxide reforming of methane were investigated in a continuous flow microreactor. The structures of the catalysts were characterized using the XRD, H2-TPR and CO2-TPD techniques. The results indicated that the CO selectivity for this reaction was very close to 100%, and the H2/CO ratio of the product gas could be controlled by changing the H2O/CO2 molar ratio of the feed gas. The simultaneous and plentiful existing of steam and CO2 had a significant influence on the catalytic performance of the 10%Ni/SBA-15 catalyst without modification. After reacting at 850 ?C for 120 h over this catalyst, the CH4 conversion dropped from 98% to 85%, and the CO2 conversion decreased from 86% to 53%. However, the 10%Ni/3%MgO/SBA-15 catalyst exhibited a much better catalytic performance, and after reacting for 620 h, the CO2 conversion over this catalyst dropped from 92% to around 77%, while the CH4 conversion was not decreased. Oxidation of the Ni0 species as well as carbon deposition during the reaction were the main reasons for the deactivation of the catalyst without modification. On the other hand, modification by the MgO promoter improved the dispersion of the Ni0 species, and enhanced the CO2 adsorption affinity which in turn depressed the occuring of carbon deposition, and thus retarded the deactivation process.

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Mechanosynthesis and mechanochemical treatment of bismuthdoped vanadium phosphorus oxide catalysts for the partial oxidation of n-butane to maleic anhydride Y. H. Taufiq-Yap*;Y. C. Wong;Y. Kamiya;W. J. Tang 2008, 17(3): 232-237.  DOI: 摘要 ( 8693 )   PDF   Three Bi-doped vanadyl pyrophosphate catalysts were prepared via dihydrate route (VPD method), which consisted of different preparation methods including mechanosynthesis, mechanochemical treatment, and the conventional reflux method. The catalysts produced by the above three methods were characterized by x-ray diffraction (XRD), scanning electron microscopy (SEM), and temperature programmed reduction (TPR). Catalytic evaluation for the partial oxidation of n-butane to maleic anhydride (MA) was also carried out. The XRD patterns of all the Bi-doped catalysts showed the main peaks of pyrophosphate phase. Lower intensity peaks were observed for VPDBiMill with two additional small peaks corresponding to the presence of a small amount of V5+ phase. The TPR profiles showed that the highest amount of active oxygen species, i.e, V4+-O- pair, responsible for n-butane activation, was removed from the mechanochemically treated Bi-doped catalyst (VPDBiMill). Furthermore, from the catalytic test results, the graph of selectivity to MA as a function of the conversion of n-butane demonstrated that VPDBiMill was the most selective catalyst. This suggests that the mechanochemical treatment of vanadium phosphate catalyst (VPDBiMill) is a potential method to improve the catalytic properties for the partial oxidation of n-butane to maleic anhydride.

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Formation of hydrogen in oxidative coupling of methane over BaCO3 and MgO catalysts Zhiming Gao*;Jiansheng Zhang;Ruiyan Wang 2008, 17(3): 238-241.  DOI: 摘要 ( 11986 )   PDF   Hydrogen formed in oxidative coupling of methane (OCM) over BaCO3 and MgO catalysts was measured since the data of H2 selectivity were missing almost in all articles published heretofore. It was found that H2 selectivity achieved about 18%, when C2 hydrocarbon's selectivity was maintained at 48% - 45% over BaCO3 catalyst at feed molar ratio of CH4/O2 = 4 in temperature range of 780 oC - 820 oC. Under similar conditions, H2 selectivity was about 14% - 16% over MgO catalyst, with C2 selectivity maintained at 41% - 42%. Possible routes for hydrogen formation in OCM reaction were discussed. Effect of addition of alkali metallic ions was also investigated.

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Deactivation studies of bifunctional Fe-HZSM5 catalyst in Fischer-Tropsch process Ali Nakhaei Pour*;Seyed Mehdi Kamali Shahri;Yahya Zamani;Mohammad Irani;Shohreh Tehrani 2008, 17(3): 242-248.  DOI: 摘要 ( 11062 )   PDF   A physical mixture of alkali-promoted iron with binder based on Fischer-Tropsch catalyst and an acidic co-catalyst (HZSM5) for syngas conversion to hydrocarbons was studied in a fixed bed micro reactor. Deactivation data were obtained during the synthesis over a 1400 h period. The deactivation studies on iron catalyst showed that this trend followed the phase transformation Fe2.2C (?) → Fe5C2 (χ) → Fe3C (θ) and the final predominant phase of the catalyst was Fe3C (θ). Deactivation of zeolite component in bifunctional catalyst may be caused by coking over the zeolitic component, dealumination of zeolite crystals, and migration of alkali promoters from iron catalyst under synthesis conditions. The deactivation rate of iron catalyst was also obtained.

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Predicting hydrate forming pressure of pure alkanes in the presence of inhibitors Alireza Bahadori*;Hari B. Vuthaluru;Saeid Mokhatab;Moses O. Tade 2008, 17(3): 249-255.  DOI: 摘要 ( 11570 )   PDF   An inherent problem with natural gas production or transmission is the formation of gas hydrates, which can lead to safety hazards, production/transportation systems, and substantial economic risks. Hydrate inhibition with different inhibitors such as, methanol, ethylene glycol (EG), triethylene glycol (TEG), and sodium chloride solution continues to play a critical role in many operations. An understanding of when the hydrates form in the presence of these hydrate inhibitors, is therefore necessary to overcome hydrate problems. Several thermodynamic models have been proposed for predicting the hydrate formation conditions in aqueous solutions containing methanol/glycols and electrolytes. However, available models have limitations that include the types of liquid, compositions of fluids, and inhibitors used. The aim of this study is to develop a simple-to-use correlation for accurate prediction of hydrate-forming pressures of pure alkanes in the presence of different hydrate inhibitors, where the obtained results illustrate good agreement with the reported experimental data.

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Effect of gallium, aluminium, and chromium on silica supported V-Mg-O catalysts during oxidative dehydrogenation of propane: Kinetic study B. Ravi Kumar*;Rajeev Kumar 2008, 17(3): 256-263.  DOI: 摘要 ( 10272 )   PDF   The oxidative dehydrogenation (ODH) of propane was conducted on gallium, aluminum, and chromium doped Si30VMgO catalysts. All catalysts were prepared and characterized. On doping, the concentrations of the phases responsible for the activity and selectivity increased in their concentrations. The reaction studies were conducted in a tubular steel reactor at temperatures of 753, 783, 813, and 843 K and atmospheric pressure. The total flow rates of the feed were chosen as 30, 40, 50, and 60 ml/min. The propane to oxygen ratios were chosen at 1 : 1, 2 : 1, and 3 : 1, respectively. The effect of various dopants on the activity and selectivity of the catalysts was studied. Deactivation studies were conducted over all the catalysts. The kinetic data were analyzed in terms of power law models and Langmuir-Hinshelwood (LH) models. The kinetic data results were analyzed by comparing the effect of dopants. Statistical model discrimination was done for the proposed models. AIC and BIC criteria were used for discrimination of the models.

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Effect of 1-butyl-3-methylimidazolium tetrafluoroborate on the formation rate of CO2 hydrate Qi Chen;Yong Yu;Peng Zeng;Wei Yang;Qianqing Liang;Xiaoming Peng;Yansheng Liu;Yufeng Hu* 2008, 17(3): 264-267.  DOI: 摘要 ( 9633 )   PDF   This paper is designed to investigate the effect of the addition of 1-butyl-3-methylimidazolium tetrafluoroborate ([C4mim][BF4]) on the formation rates of CO2 hydrates. The isothermal and isobaric methods were used to measure the formation rates of CO2 hydrates. As compared to those of pure water, the data of phase equilibrium changed greatly. The effects of pressure, temperature, and the concentration of [C4mim][BF4] aqueous solution on the formation rates of CO2 hydrates were investigated. With a constant concentration of [C4mim][BF4], the rate of gas consumption was enhanced with the lowering of experimental temperature. However, a decrease in pressure exerted an opposite effect on the rate of gas consumption. Moreover, the addition of [C4mim][BF4] raised the equilibrium pressure of hydrate formation at the same temperature.

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Selective catalytic methanation of CO in hydrogen-rich gases over Ni/ZrO2 catalyst Qihai Liu;Xinfa Dong*;Xinman Mo;Weiming Lin 2008, 17(3): 268-272.  DOI: 摘要 ( 11457 )   PDF   Ni/ZrO2 catalysts were prepared by the incipient-wetness impregnation method and were investigated in activity and selectivity for the selective catalytic methanation of CO in hydrogen-rich gases with more than 20 vol%CO2. The result showed that Ni loadings significantly influenced the performance of Ni/ZrO2 catalyst. The 1.6 wt% Ni loading catalyst exhibited the highest catalytic activity among all the catalysts in the selective methanation of CO in hydrogen-rich gas. The outlet concentration of CO was less than 20 ppm with the hydrogen consumption below 7%, at a gas-hourly-space velocity as high as 10000 h?1 and a temperature range of 260 ?C to 280 ?C. The X-ray diffraction (XRD) and temperature programmed reduction (TPR) measurements showed that NiO was dispersed thoroughly on the surface of ZrO2 support if Ni loading was under 1.6 wt%. When Ni loading was increased to 3 wt% or above, the free bulk NiO species began to assemble, which was not favorable to increase the selectivity of the catalyst.

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Selective catalytic oxidation of NO over iron and manganese oxides supported on mesoporous silica Junfeng Zhang*;Yan Huang;Xia Chen 2008, 17(3): 273-277.  DOI: 摘要 ( 9666 )   PDF   The selective catalytic oxidation (SCO) of NO was studied on a catalyst consisting of iron-manganese oxide supported on mesoporous silica (MPS) with different Mn/Fe ratios. Effects of the amount of manganese and iron, oxygen, and calcination temperature on NO conversion were also investigated. It was found that the Mn-Fe/MPS catalyst with molar ratio of Mn/Fe = 1 showed the highest activity at the calcination temperature of 400 oC. The results showed that over this catalyst, NO conversion reached 70% at 280 oC and a space velocity of 5000 h-1. SO2 and H2O had no adverse impact on the reaction activity when the SCO reaction temperature was above 240 oC. In addition, the SCO activity was suppressed gradually in the presence of SO2 and H2O below 240 oC, while such effect was reversible after heating treatment.

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Effects of CO2 content on the activity and stability of nickel catalyst supported on mesoporous nanocrystalline zirconia M. Rezaei*;S. M. Alavi;S. Sahebdelfar;Zi-Feng Yan 2008, 17(3): 278-282.  DOI: 摘要 ( 10359 )   PDF   The effects of carbon dioxide content on the catalytic performance and coke formation of nickel catalyst supported on mesoporous nanocrystalline zirconia with high surface area and pure tetragonal crystalline phase were investigated in methane reforming with carbon dioxide. The samples were characterized by XRD, BET, TPR, TPO, TPH, TEM, and SEM techniques. The catalyst prepared showed high surface area and a mesoporous structure with a narrow pore size distribution. The obtained results revealed that the increase in CO2 content increased the methane conversion and stability of the catalyst and significantly reduced the coke deposition. The TPH analysis showed that several species of carbon with different reactivities toward hydrogenation were deposited on the spent catalysts employed under different CO2 contents.

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Influence of rare-earth metal doping on the catalytic performance of CuO-CeO2 for the preferential oxidation of CO in excess hydrogen Zhigang Liu;Renxian Zhou*;Xiaoming Zheng 2008, 17(3): 283-287.  DOI: 摘要 ( 9848 )   PDF   Doping of different rare-earth metals (Pr, Nd, Y and La) had an evident influence on the catalytic performance of CuO-CeO2 for the preferential oxidation (PROX) of CO in excess hydrogen. As for Pr, the doping enhanced the catalytic activity of CuO-CeO2 for PROX. For example, the CO conversion over the above catalyst for PROX was higher than 99% at 120 oC. Especially, the doping of Pr widened the temperature window by 20 oC over CuO-CeO2 with 99% CO conversion. For Nd, Y, and La, the doping depressed the catalytic activity of CuO-CeO2 for PROX. However, the doping of transition metals markedly improved the selectivity of CuO-CeO2 for PROX.

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Effects of pretreatment and reduction on the Co/Al2O3 catalyst for CO hydrogenation Xiaoping Dai;Changchun Yu* 2008, 17(3): 288-292.  DOI: 摘要 ( 11113 )   PDF   The purpose of this study was to investigate the effect of preadsorbed CO at different temperatures, calcination temperatures, the combined influence of reduction temperature and time, and pretreatment using hydrogen or syngas as reduction agents on the F-T synthesis (FTS) activity and selectivity of Co/Al2O3 catalyst. The reactivity of the carbon species at higher preadsorption temperature with H2 in TPSR decreased, whereas the carbon-containing species showed higher reactivity over Co/Al2O3 catalyst with low calcination temperature. This agreed well with the order of catalytic activity for F-T synthesis on this catalyst. The catalytic activity of the catalyst varied with reduction temperature and time remarkably. CODEX optimization gave an optimum reduction temperature of 756 K and reduction time of 6.2 h and estimated C5+ yield perfectly. The pretreatment of Co/Al2O3 catalyst with different reduction agents (hydrogen or syngas) showed important influences on the catalytic performance. A high CO conversion and C5+ yield were obtained on the catalyst reduced by hydrogen, whereas methane selectivity on the catalyst reduced by syngas was much higher than that on the catalyst reduced by hydrogen.

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Solvent-free aerobic oxidation of ethylbenzene over supported Ni catalysts using molecular oxygen at atmospheric pressure G. Raju;P. Shiva Reddy;J. Ashok;B. Mahipal Reddy;A. Venugopal 2008, 17(3): 293-297.  DOI: 摘要 ( 10807 )   PDF   We investigated the aerobic oxidation of ethylbenzene in the absence of solvent or any additive carried out over Ni on different types of supports namely SiO2, hydroxyapatite, SBA-15, and USY Zeolites. The oxidation of ethylbenzene activities was measured in a round bottom flask immersed in oil bath at known reaction temperature. The physicochemical characteristics of the catalysts were examined by BET surface area, XRD, FT-IR and the oxidation activities were correlated with the acidities of the catalysts obtained by TPD of NH3. It was observed that both hydroxyapatite and USY (13% Na2O) supported Ni catalysts displayed higher ethylbenzene conversion and 80% selectivity towards acetophenone.

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Novel approaches for the prediction of density of glycol solutions A. Bahadori*;Y. Hajizadeh;H. B. Vuthaluru;M. O. Tade;S. Mokhatab 2008, 17(3): 298-302.  DOI: 摘要 ( 8410 )   PDF   Two new approaches for the accurate prediction of densities of the commonly used glycol solutions in the gas processing industry are presented in the article. The first approach is based on developing a simple-to-use polynomial correlation for an appropriate prediction of density of glycol solutions as a function of temperature and weight percent of glycols in water, where the obtained results show very good agreement with the reported experimental data. The second approach, however, is based on the artificial neural networks (ANN) methodology, wherein the results demonstrate the ability of the introduced method to predict reasonably accurate densities of glycols under operating conditions. Comparisons of the two novel approaches indicated that the simple-to-use correlation appears to be superior owing to its simplicity and clear numerical background, wherein the relevant coefficients can be retuned if new and more accurate data are available in the future. The average deviation of the new proposed polynomial correlation results from reported data is 0.64 kg/m3 whereas the results of artificial neural networks (ANN) methodology average deviation from reported data is 1.1 kg/m3.

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Hydrogenation of phenylpyruvic acid to phenylalanine catalyzed by Ni-B/SiO2 Qunfang Liang;Aiqing Zhang;Lin Li* 2008, 17(3): 303-308.  DOI: 摘要 ( 9961 )   PDF   Phenylalanine (Phe) is a significant amino acid that cannot be synthesized by people themselves but must be taken from environment. It was initially found that the nanosized amorphous Ni-B/SiO2 alloy prepared by the chemical reduction method was an effective catalyst for the preparation of Phe from phenylpyruvic acid (PPA) by amination and hydrogenation. It has been found that the amorphous Ni-B/SiO2 alloy catalyst exhibits superior activity and selectivity to the traditional catalysts Raney Ni and Urushibara nickel. The effects of reaction time, amounts of catalysts and ammonia solution, reaction temperature, and H2 pressure on the reaction have been investigated systematically. The results indicated that the yield of Phe was 97.9%, and the selectivity for Phe reached 98.9% when the reaction was carried out for 3 h at 333 K and 2.0 MPa of H2 with m(Cat.) :m(PPA) = 0.6 : 1.0 and n(NH3) : n(PPA) = 3 : 1. The catalysts were characterized by XRD, AAS, XPS, BET, and TEM, and the relationship between the catalyst structure and the catalytic activity was discussed in detail. It was found that the reason why Ni-B/SiO2 amorphous alloy catalyst was much more active for the preparation of Phe could be accounted for by the presence of electron-rich Ni due to electron donation from alloying B; the smaller size of Ni-B particles, the larger specific surface area of Ni-B/SiO2.

Reviews

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Direct oxidation of methane to oxygenates over heteropolyanions Ouarda Benlounes;Sadia Mansouri;Chérifa Rabia;Smain Hocine* 2008, 17(3): 309-312.  DOI: 摘要 ( 10346 )   PDF   Partial oxidation of methane to formaldehyde and methanol was studied at atmospheric pressure in the temperature range of 700--750 oC using heteropolycompound catalysts (NH4)6HSiMo11FeO40, (NH4)4PMo11FeO39, and H4PMo11VO40, which were prepared and characterized by various analysis techniques such as infrared, visible UV, DRX, ATG/ATD. O2 or N2O was used as the oxidizing agent, and the principal products of the reaction were CH3OH, CH2O, CO, CO2, and water. The conversion and the selectivity of products depend strongly on the reaction temperature, the nature of oxidizing agent, and the composition of catalyst.