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2011, Vol. 20, No. 1　Online: 2011-01-30

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Methane reforming with CO2 to syngas over CeO2-promoted Ni/Al2O3-ZrO2 catalysts prepared via a direct sol-gel process Hansheng Li*, Hang Xu, Jinfu Wang 2011, 20(1): 1-8.  DOI: 10.1016/S1003-9953(10)60156-9 摘要 ( 11578 )   CeO2-promoted Ni/Al2O3-ZrO2 (Ni/Al2O3-ZrO2-CeO2) catalysts were prepared by a direct sol-gel process with citric acid as gelling agent. The catalysts used for the methane reforming with CO2 was studied by infrared spectroscopy (IR), thermal gravimetric analysis (TGA), microscopic analysis, X-ray diffraction (XRD) and temperature-programmed reduction (TPR). The catalytic performance for CO2 reforming of methane to synthesis gas was investigated in a continuous-flow micro-reactor under atmospheric pressure. TGA, IR, XRD and microscopic analysis show that the catalysts prepared by the direct sol-gel process consist of Ni particles with a nanostructure of around 5 nm and an amorphous-phase composite oxide support. There exists a chemical interaction between metallic Ni particles and supports, which makes metallic Ni well dispersed, highly active and stable. The addition of CeO2 effectively improves the dispersion and the stability of Ni particles of the prepared catalysts, and enhances the adsorption of CO2 on the surface of catalysts. The catalytic tests for methane reforming with CO2 to synthesis gas show that the Ni/Al2O3-ZrO2-CeO2 catalysts show excellent activity and stability compared with the Ni/Al2O3 catalyst. The excellent catalytic activity and stability of the Ni/Al2O3-ZrO2-CeO2 are attributed to the highly, uniformly and stably dispersed small metallic Ni particles, the high reducibility of the Ni oxides and the interaction between metallic Ni particles and the composite oxide supports.

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Kinetics modeling for the mixed reforming of methane over Ni-CeO2/MgAl2O4 catalyst Hye Jin Jun, Myung-June Park*, Seung-Chan Baek, Jong Wook Bae, Kyoung-Su Ha, Ki-Won Jun 2011, 20(1): 9-17.  DOI: 10.1016/S1003-9953(10)60148-X 摘要 ( 10281 )   Kinetics model was developed for the mixed (steam and dry) reforming of methane, which is useful for the control of H2/CO ratio. The equilibrium constants of reaction rate were determined using the experimental equilibrium data at different reaction temperatures, while the forward reaction rate constants were estimated using the experimental data under non-equilibrium (high inert fraction and high space velocity) conditions. The comparison between calculated and experimental data clearly showed that the developed model described satisfactorily, and further analysis using the parametric sensitivity determined the wall temperature and CO2 fraction in the feed gas as effective parameters for the manipulation of CH4 conversion and H2/CO ratio of synthesis gas under the equilibrium condition. Meanwhile, the inert fraction, rather than the residence time, was selected as additional parameter under non-equilibrium condition.

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Esterification of levulinic acid ton-butyl levulinate over heteropolyacid supported on acid-treated clay S. Dharne, V. V. Bokade* 2011, 20(1): 18-24.  DOI: 10.1016/S1003-9953(10)60147-8 摘要 ( 9040 )    Levulinic acid has been identified as a promising green, biomass-derived platform chemical. n-Butyl levulinate is used as an important intermediate having diverse applications. The present work focuses on the synthesis ofn-butyl levulinate by esterification of levulinic acid withn-butanol using heteropolyacid (HPA) supported on acid-treated clay montmorillonite (K10). 20% (w/w) dodecatungestophosphoric acid (DTPA) supported on K10 was found to be the most efficient catalyst with 97% levulinic acid conversion and 100% selectivity towards n-butyl levulinate. Effects of various process parameters were studied to examine the efficacy of 20% (w/w) DTPA/K10 for optimization of the activity.

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Comparison and application of different empirical correlations for estimating the hydrate safety margin of oil-based drilling fluids containing ethylene glycol Fulong Ning*, Ling Zhang, Guosheng Jiang*, Yunzhong Tu, Xiang Wu, Yibing Yu 2011, 20(1): 25-33.  DOI: 10.1016/S1003-9953(10)60161-2 摘要 ( 12353 )   As the oil and gas industries continue to increase their activity in deep water, gas hydrate hazards will become more serious and challenging, both at present and in the future. Accurate predictions of the hydrate-free zone and the suitable addition of salts and/or alcohols in preparing drilling fluids are particularly important both in preventing hydrate problems and decreasing the cost of drilling operations. In this paper, we compared several empirical correlations commonly used to estimate the hydrate inhibition effect of aqueous organic and electrolyte solutions using experiments with ethylene glycol (EG) as a hydrate inhibitor. The results show that the Najibi et al. correlation (for single and mixed thermodynamic inhibitors) and the Ostergaard et al. empirical correlation (for single thermodynamic inhibitors) are suitable for estimating the hydrate safety margin of oil-based drilling fluids (OBDFs) in the presence of thermodynamic hydrate inhibitors. According to the two correlations, the OBDF, composed of 1.6 L vaporizing oil, 2% emulsifying agent, 1% organobentonite, 0.5% SP-1, 1% LP-1, 10% water and 40% EG, can be safely used at a water depth of up to 1900 m. However, for more accurate predictions for drilling fluids, the effects of the solid phase, especially bentonite, on hydrate inhibition need to be considered and included in the application of these two empirical correlations.

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Adsorption of cyclohexene and its dehydrogenation intermediates on nAu/Pt(100)(n = 0, 1, 2) surfaces: A DFT study Hongyan Ma, Wenge Xu, Zhenfeng Shang*, Guichang Wang 2011, 20(1): 34-40.  DOI: 10.1016/S1003-9953(10)60143-0 摘要 ( 11426 )   Adsorption of cyclohexene and its dehydrogenation intermediates on the nAu/Pt(100) (n = 0, 1, 2 means clean Pt, one monolayer and two layers of Au covered Pt surfaces, respectively.) has been investigated by self-consistent (GGA-PW91) density functional theory combined with periodic slab model. It is found that on the clean platinum, there are two kinds of favorable adsorption sites, i.e., hollow sites and bridge sites, and the adsorption energy at the hollow site is larger than that at the bridge site. However, on the Au/Pt and 2Au/Pt surfaces, there are three kinds of adsorption sites, and the adsorption energies are alike at both the bridge site and the top site. The magnitude order of the adsorption energies is as follows: clean Pt > Au/Pt > 2Au/Pt. The configurations of cyclohexene molecule have been distorted a little during the geometry optimizations. The lengths of C--M (M = Pt or Au, on the top layer of the slab) bonds are closely related to the corresponding adsorption energies.

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Effects of preparation conditions of Au/FeOx/Al2O3 catalysts prepared by a modified two-step method on the stability for CO oxidation Xuhua Zou*, Jinguang Xu, Shixue Qi, Zhanghuai Suo, Lidun An, Feng Li 2011, 20(1): 41-47.  DOI: 10.1016/S1003-9953(10)60150-8 摘要 ( 10936 )   Composite oxide FeOx/Al2O3-supported gold catalysts were prepared by a modified two-step method. The effects of preparation conditions on the initial catalytic activity and long-time stability were studied for CO oxidation. XRD, XPS and in situ FTIR were employed to investigate the state of FeOx and the species on the catalyst surface. The results showed that Au/FeOx/Al2O3 catalysts prepared by this method exhibited high activity and high stability in a wide pH value range. Calcination pretreatment was proved to be beneficial to improving the activity and stability. The beneficial effects of FeOx acting as a structural promoter could be ascribed to the ability to supply active oxygen species. As the precursor of FeOx, Fe(NO3)3 is superior to FeCl3 for obtaining higher stability.

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Catalytic properties of Cu-Co catalysts supported on HNO3-pretreated CNTs for higher-alcohol synthesis Limin Shi*, Wei Chu*, Siyu Deng 2011, 20(1): 48-52.  DOI: 10.1016/S1003-9953(10)60145-4 摘要 ( 11912 )   HNO3-pretreated CNTs were employed as supports, and a special ultrasound-assisted impregnation method was designed to prepare supported Cu-Co catalysts for higher-alcohol synthesis from syngas. The catalysts used in this work were characterized by N2 adsorption-desorption, TEM, XRD, H2-TPR, CO-TPD techniques. It was found that the pre-treatment procedure of CNTs remarkably promoted the catalytic properties of the Cu-Co/CNTs catalysts. For the Cu-Co catalyst supported on CNTs pre-treated by 68 wt% HNO3, some active components were introduced into the CNTs channels, their dispersions and the amount of strongly adsorbed CO-species were improved. The CO conversion and alcohol yield on the HNO3-pretreated Cu-Co/CNTs catalyst were increased by ~21% and ~69%, respectively, compared with those on the normal Cu-Co/CNTs catalyst.

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Selective hydrogenation of benzene to cyclohexene on Ru-based catalysts promoted with Mn and Zn Xiaoli Zhou, Haijie Sun, Wei Guo, Zhongyi Liu*, Shouchang Liu 2011, 20(1): 53-59.  DOI: 10.1016/S1003-9953(10)60152-1 摘要 ( 12788 )   Ru-based catalysts promoted with Mn and Zn were prepared by a co-precipitation method. In liquid-phase hydrogenation of benzene, the Ru-Mn-Zn catalysts exhibited superior catalytic performance to the catalysts promoted with Zn or Mn alone. The optimum Mn/Zn molar ratio was determined to be 0.3. With the addition of 0.5 g NaOH, the Ru-Mn-Zn-0.3 catalyst, which was reduced at 150 ℃, afforded a cyclohexene selectivity of 81.1% at a benzene conversion of 60.2% at 5 min and a maximum cyclohexene yield of 59.9% at 20 min. Based on characterizations, the excellent performance of Ru-Mn-Zn catalyst was ascribed to the suitable pore structure, the appropriate reducibility and the homogenous chemical environment of the catalyst.

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Study of CO adsorption on perfect and defective pyrite(100) surfaces by density functional theory Yudong Du, Wenkai Chen*, Yongfan Zhang, Xin Guo 2011, 20(1): 60-64.  DOI: 10.1016/S1003-9953(10)60146-6 摘要 ( 11245 )   First-principles calculations based on density functional theory (DFT) and the generalized gradient approximation (GGA) have been used to study the adsorption of CO molecule on the perfect and defective FeS2(100) surfaces. The defective Fe2S(100) surfaces are caused by sulfur deficiencies. Slab geometry and periodic boundary conditions are employed with partial relaxations of atom positions in calculations. Two molecular orientations, C- and O-down, at various distinct sites have been considered. Total energy calculations indicated that no matter on perfect or deficient surfaces, the Fe position is relatively more favored than the S site with the predicted binding energies of 120.8 kJ/mol and 140.8 kJ/mol, respectively. Moreover, CO was found to be bound to Fe atom in vertical configuration. The analysis of density of states and vibrational frequencies before and after adsorption showed clear changes of the C--O bond.

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Studies on accelerated deactivation of ruthenium-promoted alumina-supported alkalized cobalt Fischer-Tropsch synthesis catalyst Shohreh Tehrani, Mohamad Irani, Ahmad Tavasoli*, Yadollah Mortazavi, Abbas A. Khodadadi, Ali Nakhaei Pour 2011, 20(1): 65-71.  DOI: 10.1016/S1003-9953(10)60144-2 摘要 ( 16495 )   Accelerated deactivation of ruthenium-promoted alumina-supported alkalized cobalt (K-Ru-Co/γ-Al2O3) Fischer-Tropsch (FT) synthesis catalyst along the catalytic bed over 120 h of time-on-stream (TOS) was investigated. Catalytic bed was divided into three parts and structural changes of the spent catalysts collected from each catalytic bed after FT synthesis were studied using different techniques. Rapid deactivation was observed during the reaction due to high reaction temperature and low feed flow rates. The physico-chemical properties of the catalyst charged in the Bed\#1 of the reactor did not change significantly. Interaction of cobalt with alumina and the formation of CoAl2O4 increased along the catalytic bed. Reducibility percentage decreased by 4.5%, 7.5% and 12.9% for the catalysts in the Beds\#1, \#2 and\#3, respectively. Dispersion decreased by 8.8%, 14.4% and 26.6% for the catalysts in the Beds\#1, \#2 and\#3, respectively. Particle diameter increased by 0.6%, 2.4% and 10.4% for the catalysts in the Beds\#1, \#2 and\#3, respectively, suggesting higher rate of sintering at the last catalytic bed. The amount of coke at the last catalytic bed was significantly higher than those of Beds\#1 and\#2.

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Preparation and properties of magnetic alumina microspheres with a γ-Fe2O3/SiO2 core and Al2O3 shell Qingtao Fu, Tingting He, Lianqing Yu, Yongming Chai, Chenguang Liu 2011, 20(1): 72-76.  DOI: 10.1016/S1003-9953(10)60155-7 摘要 ( 11281 )   Magnetic alumina composite microspheres with γ-Fe2O3 core/Al2O3 shell structure were prepared by the oil column method. A dense silica layer was deposited on the surface of γ-Fe2O3 particles (denoted as γ-Fe2O3/SiO2) with a desired thickness to protect the iron oxide core against acidic or high temperature conditions. γ-Fe2O3/SiO2/Al2O3 particles with about 85 wt% Al2O3 were obtained and showed to be suitable for practical applications as a magnetic catalyst or catalyst support due to their magnetic properties and pore structure. The products were characterized with scanning electron microscope (SEM) and transmission electron microscope (TEM), nitrogen adsorption-desorption, and vibrating sample magnetometer (VSM). The specific surface area and pore volume of the γ-Fe2O3/SiO2/Al2O3 composite microspheres calcined at 500 ℃ were 200 m2/g and 0.77 cm3/g, respectively.

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Potassium-decorated active carbon supported Co-Mo-based catalyst for water-gas shift reaction Yixin Lian, RuiFen Xiao, Weiping Fang, Yiquan Yang 2011, 20(1): 77-83.  DOI: 10.1016/S1003-9953(10)60154-5 摘要 ( 10706 )   The effect of potassium-decoration was studied on the activity of water-gas shift (WGS) reaction over the Co-Mo-based catalysts supported on active carbon (AC), which was prepared by incipient wetness co-impregnation method. The decoration of potassium on active carbon in advance enhances the activities of the CoMo-K/AC catalysts for WGS reaction. Highest activity (about 92% conversion) was obtained at 250 ℃ for the catalyst with an optimum K2O/AC weight ratio in the range from 0.12 to 0.15. The catalysts were characterized by TPR and EPR, and the results show that activated carbon decorated with potassium makes Co-Mo species highly dispersed, and thus easily reduced and sulfurized. XRD results show that an appropriate content of potassium-decoration on active carbon supports may favors the formation of highly dispersed Co9S8-type structures which are situated on the edge or a site in contact with MoS2, K-Mo-O-S, Mo-S-K phase. Those active species are responsible for the high activity of CoMo-K/AC catalysts.

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A parametric study of methane decomposition into carbon nanotubes over 8Co-2Mo/Al2O3 catalyst Siang-Piao Chai, Choon-Ming Seah, Abdul Rahman Mohamed 2011, 20(1): 84-89.  DOI: 10.1016/S1003-9953(10)60151-X 摘要 ( 13344 )   The effects of reaction temperature, partial pressure of methane, catalyst weight and gas hourly space velocity (GHSV) on methane decomposition were reported. The decomposition reaction was performed in a vertical fixed-bed reactor over 8Co-2Mo/Al2O3 catalyst. The experimental results show that these four process parameters studied had vital effects on carbon yield. As revealed by the electron microscopy and Raman spectroscopy analyses, the reaction temperature and GHSV governed the average diameter, the diameter distribution and the degree of graphitization of the synthesized carbon nanotubes (CNTs). Also, an evidence is presented to show that higher temperatures and higher GHSV favored the formation of better-graphitized CNTs with larger diameters.

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Why is metallic Pt the best catalyst for methoxy decomposition? Ruipeng Ren, Cuiyu Niu, Shaoyue Bu, Yuhua Zhou, Yongkang Lv*, Guichang Wang 2011, 20(1): 90-98.  DOI: 10.1016/S1003-9953(10)60158-2 摘要 ( 12327 )   The decomposition of methoxy on Cu(111), Ag(111), Au(111), Ni(111), Pt(111), Pd(111), and Rh(111) has been studied in detail by the density functional theory calculations. The calculated activation barriers were successfully correlated with the coupling matrix element V2ad and the d-band center (εd) for the group IB metals and group VIII metals, respectively. By comparison of the activation energy barriers of the methoxy decomposition on different metals, it was found that Pt is the best catalyst for methoxy decomposition. The possible reason why the metallic Pt is the best catalyst has been analyzed from both the energetic data and the electronic structure information, that is, methoxy decomposition on Pt(111) has the largest exothermic behavior due to the closest p-band center of the CH3O among all metals after the adsorption.

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Multiobjective optimization scheme for industrial synthesis gas sweetening plant in GTL process Alireza Behroozsarand*, Akbar Zamaniyan 2011, 20(1): 99-109.  DOI: 10.1016/S1003-9953(10)60153-3 摘要 ( 10137 )   In industrial amine plants the optimized operating conditions are obtained from the conclusion of occurred events and challenges that are normal in the working units. For the sake of reducing the costs, time consuming, and preventing unsuitable accidents, the optimization could be performed by a computer program. In this paper, simulation and parameter analysis of amine plant is performed at first. The optimization of this unit is studied using Non-Dominated Sorting Genetic Algorithm-II in order to produce sweet gas with CO2 mole percentage less than 2.0% and H2S concentration less than 10 ppm for application in Fischer-Tropsch synthesis. The simulation of the plant in HYSYS v.3.1 software has been linked with MATLAB code for real-parameter NSGA-II to simulate and optimize the amine process. Three scenarios are selected to cover the effect of (DEA/MDEA) mass composition percent ratio at amine solution on objective functions. Results show that sour gas temperature and pressure of 33.98 ℃ and 14.96 bar, DEA/CO2 molar flow ratio of 12.58, regeneration gas temperature and pressure of 94.92 ℃ and 3.0 bar, regenerator pressure of 1.53 bar, and ratio of DEA/MDEA = 20%/10% are the best values for minimizing plant energy consumption, amine circulation rate, and carbon dioxide recovery.