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2007, Vol. 16, No. 3　Online: 2007-09-30

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Reviews

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Chemical Reduction of CO2 to Different Products during Photo Catalytic Reaction on TiO2 under Diverse Conditions: an Overview G. R. Dey* 2007, 16(3): 217-226.  DOI: 摘要 ( 9844 )   PDF   The chemical reduction of CO2 remains a challenge with respect to the reversal of the oxidative degradation of any organic materials. The conversion of CO2 into useful substances is essential in developing alternative fuels and various raw materials for different industries. This also aids in preventing the continuous rise in tropospheric temperature due to the green house effect of CO2. In this article an overview of the growth taken place so far in the field of CO2 chemical reduction is presented. The discussion comprises of photochemical methods for the development of different products, viz. CO, CH3OH and CH4, through chemical reduction of CO2. This includes the use of photo catalysts, mainly TiO2, and the role of a hole scavenger (such as 2-propanol) for this purpose.

Articles

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The Effect of Nb Loading on Catalytic Properties of Ni/Ce0.75Zr0.25O2 Catalyst for Methane Partial Oxidation Sitthiphong Pengpanich*;Vissanu Meeyoo;Thirasak Rirksomboon;Johannes Schwank 2007, 16(3): 227-234.  DOI: 摘要 ( 11857 )   PDF   In this study, the effect of Nb loading on the catalytic activity of Ce0.75Zr0.25O2-supported Ni catalysts was studied for methane partial oxidation. The catalysts were characterized by BET, H2 chemisorption, XRD, TPR, TEM and tested for methane partial oxidation to syngas in the temperature range of 400−800 ℃ at atmospheric pressure. The results showed that the activity of methane partial oxidation on the catalysts was apparently dependent on Nb loading. It seemed that the addition of Nb lowered the catalytic activity for methane partial oxidation and increased the extent of carbon deposition. This might be due to the strong interaction between NiO and Nb-modified support and reduction of surface oxygen reducibility.

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Carbon Dioxide/Methane Separation by Adsorption on Sepiolite Jose A. Delgado*;Maria A. Uguina;Jose L. Sotelo;Beatriz Ruiz;Marcio Rosario 2007, 16(3): 235-243.  DOI: 摘要 ( 8694 )   PDF   The methanol conversion over Fe-Zn-Zr catalyst was studied at 0.1 MPa and 280−360 ℃. The experimental results indicate that the main products of methanol conversion are methane and butane, and that other hydrocarbons are scarcely produced. All results show that propylene is most probably the olefin formed first in methanol conversion rather than ethene over Fe-Zn-Zr catalyst. Methane is formed from methoxy group, and C4 is possibly yielded on the surface from propylene through binding with a methoxy group.

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Effect of Manganese Incorporation Manner on an Iron-Based Catalyst for Fischer-Tropsch Synthesis Tingzhen Li;Yong Yang;Chenghua Zhang;Zhichao Tao;Haijun Wan;Xia An;Hongwei Xiang*;Yongwang Li 2007, 16(3): 244-251.  DOI: 摘要 ( 9812 )   PDF   A systematic study was undertaken to investigate the effects of the manganese incorporation manner on the textural properties, bulk and surface phase compositions, reduction/carburization behaviors, and surface basicity of an iron-based Fischer-Tropsch synthesis (FTS) catalyst. The catalyst samples were characterized by N2 physisorption, X-ray photoelectron spectroscopy (XPS), H2 (or CO) temperature-programmed reduction (TPR), CO2 temperature-programmed desorption (TPD), and MÖssbauer spectroscopy. The FTS performance of the catalysts was studied in a slurry-phase continuously stirred tank reactor (CSTR). The characterization results indicated that the manganese promoter incorporated by using the coprecipitation method could improve the dispersion of iron oxide, and decrease the size of the iron oxide crystallite. The manganese incorporated with the impregnation method is enriched on the catalyst’s surface. The manganese promoter added with the impregnation method suppresses the reduction and carburization of the catalyst in H2, CO, and syngas because of the excessive enrichment of manganese on the catalyst surface. The catalyst added manganese using the coprecipitation method has the highest CO conversion (51.9%) and the lowest selectivity for heavy hydrocarbons (C12+).

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Study of Hydrogen Adsorption on Pt/WO3-ZrO2 through Pt Sites Sugeng Triwahyono;Aishah Abdul Jalil;Hideshi Hattori 2007, 16(3): 252-257.  DOI: 摘要 ( 9809 )   PDF   The rate determining step and the energy barrier involved in hydrogen adsorption on Pt/WO3- ZrO2 were studied based on the assumption that the hydrogen adsorption occurs only through Pt sites. The rate of hydrogen adsorption on Pt/WO3-ZrO2 was measured in the adsorption temperature range of 323−573 K and an initial hydrogen pressure of 50 Torr. The rates of hydrogen uptake were very high for the initial few minutes and the adsorption continued for more than 5 h below 523 K. The hydrogen uptake far exceeded the H/Pt ratio of unity for all adsorption temperatures, indicating that the adsorption of hydrogen involved the dissociative adsorption of hydrogen on Pt sites to form hydrogen atoms, the spillover of hydrogen atoms onto the surface of the WO3-ZrO2 catalyst, the diffusion of spiltover hydrogen atom over the surface of the WO3-ZrO2 catalyst, and the formation of protonic acid site originated from hydrogen atom by releasing an electron in which the electron may react with a second hydrogen atom to form a hydride near the Lewis acid site. The rate determining step was the spillover with the activation energy of 12.3 kJ/mol. The rate of hydrogen adsorption cannot be expressed by the rate equation based on the assumption that the rate determining step is the surface diffusion. The activity of Pt/WO3-ZrO2 was examined on n-heptane isomerization in which the increase of hydrogen partial pressure provided positive-effect on the conversion of n-heptane and negative-effect on the selectivity towards iso-heptane.

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Catalytic Combustion of Methane over High Copper-Loading ZSM-5 Catalysts Ogtour M’Ramadj;Bo Zhang;Dao Li;Xingyi Wang;Guanzhong Lu 2007, 16(3): 258-265.  DOI: 摘要 ( 10942 )   PDF   Two series of Cu/ZSM-5 catalysts, loading from 5 to 20 wt% CuO, were prepared by the deposition-precipitation and impregnation methods, respectively. The catalysts prepared by the impregnation method showed better catalytic performances than those prepared by the deposition-precipitation method and the increase of copper loading favored methane conversion. 20Cu(I)/ZSM-5 had the highest activity with T90% of 746 K, and for 20Cu(D)/ZSM-5, T90% was as high as 804 K. The characterization of X-ray diffraction (XRD), temperature-programmed reduction (TPR), temperature-programmed desorption (TPD), and X-ray photoelectron spectroscopy (XPS) revealed that the dispersion of copper species could be improved by using the deposition-precipitation method instead of the impregnation method, but the fraction of surface CuO, corresponding to active sites for methane oxidation, was larger on 20Cu(I)/ZSM-5 than 20Cu(D)/ZSM-5. The results of Pyridine-Fourier transform infrared spectrum (Py-FT-IR) showed that a majority of Lewis acidity and a minority of Brønsted acidity were present on Cu/ZSM-5 catalysts. 20Cu(I)/ZSM-5 presented more Lewis acid sites. The number of Lewis acid sites changed significantly with preadsorption of oxygen. Adsorption of methane and oxygen on acid sites was observed. The properties of Cu/ZSM-5 catalysts were correlated with the activity for methane oxidation.

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n-Butane Oxidation over γ-Al2O3 Supported Vanadium Phosphate Catalysts Y. H. Taufiq-Yap*;L. K. Leong;R. Irmawati 2007, 16(3): 266-272.  DOI: 摘要 ( 9319 )   PDF   Four vanadium phosphate catalysts supported on -Al2O3 (20 wt%) were synthesized via wetness impregnation of VOHPO4·0.5H2O precursor and calcined for different durations (6, 10, 30 and 75 h) at 673 K in a reaction flow of n-butane/air mixture. The samples calcined for 6 and 10 h produced only a single phase of (VO)2P2O7. However, the VOPO4 phase (-VOPO4) was detected and became more prominent with only a minor pyrophosphate peaks were found after 30 h of calcination. All these pyrophosphate peaks disappeared after 75 h of calcination. The formation of V5+ phase was also observed in the SEM micrographs. The redox properties and the nature of oxidants of the catalysts employed in this study were investigated by H2-TPR analysis. Selective oxidation of n-butane to maleic anhydride (MA) over these catalysts shows that the percentage of n-butane conversion decreases with the transformation of the catalysts from V4+ to V5+ phases. An appropriate ratio of V5+/V4+ can enhance the performance of the VPO catalyst. However, a higher amount of V5+ and its associated oxygen species are responsible to promote the MA selectivity.

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Carbon Dioxide Fixation Method for Electrosynthesis of Benzoic Acid from Chlorobenzene A. J. Aishah*;M. A. Hartini;S. Normala;A. M. Norhuda;H. H. N Hanis;H. M. Razif;T. Sugeng 2007, 16(3): 273-277.  DOI: 摘要 ( 10236 )   PDF   Carbon dioxide fixation technique was developed as an alternative dechlorination method of chlorobenzenes. Electrolysis of chlorobenzene was carried out in a one-compartment cell fitted with an aluminium anode and a platinum cathode. Electrolysis in N,N-dimethylformamide (DMF) solution containing 0.1 M of tetrapropylammonium bromide (TPAB) at 0 ℃, 100 ml/min of CO2 flow rate and 120 mA/cm2 of current density was found to be the optimum conditions of this electrocarboxylation, which gave 72% yield of benzoic acid from chlorobenzene. These conditions were then applied to 1,2-dichlorobenzene and 1,3-dichlorobenzene in order to convert them to their corresponding benzoic acids.

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Study of Manganese Promoter on a Precipitated Iron-Based Catalyst for Fischer-Tropsch Synthesis Zhichao Tao;Yong Yang*;Chenghua Zhang;Tingzhen Li;Mingyue Ding;Hongwei Xiang;Yongwang Li 2007, 16(3): 278-285.  DOI: 摘要 ( 10173 )   PDF   The effects of Manganese (Mn) incorporation on a precipitated iron-based Fischer-Tropsch synthesis (FTS) catalyst were investigated using N2 physical adsorption, air differential thermal analysis (DTA), H2 temperature-programmed reduction (TPR), and MÖssbauer spectroscopy. The FTS performances of the catalysts were tested in a slurry phase reactor. The characterization results indicated that Mn increased the surface area of the catalyst, and improved the dispersion of -Fe2O3 and reduced its crystallite size as a result of the high dispersion effect of Mn and the Fe-Mn interaction. The Fe-Mn interaction also suppressed the reduction of -Fe2O3 to Fe3O4, stabilized the FeO phase, and (or) decreased the carburization degree of the catalysts in the H2 and syngas reduction processes. In addition, incorporated Mn decreased the initial catalyst activity, but improved the catalyst stability because Mn restrained the reoxidation of iron carbides to Fe3O4, and improved further carburization of the catalysts. Manganese suppressed the formation of CH4 and increased the selectivity to light olefins (C= 2−4), but it had little effect on the selectivities to heavy (C5+) hydrocarbons. All these results indicated that the strong Fe-Mn interaction suppressed the chemisorptive effect of the Mn as an electronic promoter, to some extent, in the precipitated iron-manganese catalyst system.

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Catalytic Systems Containing p-Toluenesulfonic Acid for the Coupling Reaction of Formaldehyde and Methyl Formate Kebing Wang;Jie Yao;Yue Wang;Gongying Wang* 2007, 16(3): 286-292.  DOI: 摘要 ( 10125 )   PDF   The coupling reaction of formaldehyde (FA) and methyl formate (MF) to form methyl glycolate (MG) and methyl methoxy acetate (MMAc), catalyzed by p-toluenesulfonic acid (p-TsOH) as well as assisted by different kinds of solvents or Ni-containing compounds, had been investigated. The results showed that when the reaction was carried out at 140 ℃, with a molar ratio of FA to MF of 0.65 : 1, molar fraction of p-TsOH to total feedstock of 11.0%, and reaction time of 3 h, the yield of MG and MMAc was 31.1% and 17.1%, respectively. p-TsOH catalyzed the coupling reaction by means of the synergistic catalysis of protonic acidity and soft basicity. Adding extra solvents to the reaction system was unfavorable for the reaction. The composite catalytic system consisting of p-TsOH and NiX2 (X=Cl, Br, I) exhibited a high catalytic performance for the coupling reaction, and NiX2 acted as a promoter in the reaction, whose promotion for the catalysis increased in the following order: NiCl2

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The Possibility of Wax Formation in Gas Fields: a Case Study Z. Jeirani;A. Lashanizadegan;Sh. Ayatollahi*;J. Javanmardi 2007, 16(3): 293-300.  DOI: 摘要 ( 8852 )   PDF   Natural gas production from a gas reservoir (Reservoir A) located in the south of Iran, presents solids deposition during processing because the condensate contains suspended and dissolved solids. Solids deposition occurs not only in the transportation lines from the wells to the separators but also in the various operating units of gas streams and condensate stream. In this study, the multisolid-phase model has been used to predict the wax precipitation from gas and gas condensate fluids. The properties of gas and liquid phases are described using the Soave-Redlich-Kwong (SRK) equation of state. The model is then used to predict the possibility of the wax formation in Reservoir A gas facilities, located at the south of Iran. Solid deposition which occurred in the various streams of that facility confirmed the calculated results. Finally, the wax appearance temperature (WAT), the weight percent of wax formation and the effects of pressure and temperature on the wax formation were also predicted.

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Studies on Catalytic Conversion of Ethylene Fuyu Liu;Chunyi Li*;Xue Ding;Xinghua You; 2007, 16(3): 301-307.  DOI: 摘要 ( 9160 )   PDF   FCC dry gas contains a large amount of ethylene. It is used by most of the refineries in China as fuel or simply burned in atmosphere. Few refineries make good use of the dry gas, so the precious ethylene resource in the dry gas is wasted. In this article, the possibility of catalytic conversion of ethylene to C3, C4, and some high molecular weight hydrocarbons in a fixed bed micro-reactor using LTB-1 catalyst, with pure ethylene as feedstock was studied. Effects of reaction temperature, reaction pressure, and feedstock flow rate, on the conversion of ethylene and the distribution of products were investigated to determine the proper reaction parameters to be used in practice. Good results indicate that this study may provide a new way of using the ethylene resource in the FCC dry gas.

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Pretreatment of Alumina and Its Influence on the Properties of Co/Alumina Catalysts for Fischer-Tropsch Synthesis Chen Li;Qiwen Sun;Fahai Cao;Weiyong Ying*;Dingye Fang 2007, 16(3): 308-315.  DOI: 摘要 ( 9502 )   PDF   16.6%Co/ -Al2O3 catalysts prepared by incipient wetness impregnation method were used for Fischer-Tropsch synthesis. The support was pre-treated with different concentration of NH4NO3 aqueous solution. The effect of support pre-treatment on the properties of support and performance of supportedcobalt- based catalysts was investigated. To treat the support with NH4NO3 aqueous solution enlarged the pore of -Al2O3, decreased the impurity Na2O content, and weakened the surface acidity of -Al2O3. The change in the properties of the support decreased the interaction between cobalt species and support, enhanced the CO hydrogenation rate and the C5+ selectivity. For all catalysts, increasing the reaction temperature increased the CO hydrogenation rate or the CO conversion, slightly decreased the total hydrocarbon selectivity, and favored the formation of methane and light hydrocarbons, while the chain growth probability decreased. For 16.6%Co/ -Al2O3 catalysts, prepared with the support treated with 100 g/L NH4NO3 aqueous solution, the CO conversion, the CH4 selectivity, and the C5+ selectivity were 83.13%, 6.86% and 82.75% respectively, and the chain growth probability was 0.83 under the condition of 493 K, 1.5 MPa, 500 h.1 and the molar ratio of H2 to CO being 2.0 in feed.

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In-Situ FT-IR Investigation of Partial Oxidation of Methane to Syngas over Rh/SiO2 Catalyst Tinghua Wu*;Dongmin Lin;Ying Wu;Xiaoping Zhou;Qiangu Yan;Weizheng Weng;Huilin Wan; 2007, 16(3): 316-321.  DOI: 摘要 ( 12255 )   PDF   Partial oxidation of methane to syngas (POM) over Rh/SiO2 catalyst was investigated using in-situ FT-IR. When methane interacted with 1.0wt%Rh/SiO2 catalyst, it was dissociated to adsorbed hydrogen and CHx species. The adsorbed hydrogen atoms were transferred to SiO2 surface by “spill-over” and reacted with lattice oxygen to form surface −OH species. POM mechanism was investigated over Rh/SiO2 catalyst using in-situ FT-IR. It was found that CO2 was formed before CO could be detected when CH4 and O2 were introduced over the preoxidized Rh/SiO2 catalyst, whereas CO was detected before CO2 was formed over the prereduced Rh/SiO2 catalyst.

Communctions

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Catalytic Oxidation of Dimethyl Ether to Dimethoxymethane over Cs Modified H3PW12O40/SiO2 Catalysts Qingde Zhang;Yisheng Tan;Caihong Yang;Yizhuo Han*;Jun Shamoto;Noritatsu Tsubaki 2007, 16(3): 322-325.  DOI: 摘要 ( 9912 )   PDF   The attractive utilization route for one-step catalytic oxidation of dimethyl ether to dimethoxymethane was successfully carried out over the H3PW12O40(40%)/SiO2 catalyst, modified by Cs, K, Ni, and V. The Cs modification of H3PW12O40(40%)/SiO2 gave the most promising result of 20% dimethyl ether conversion and 34.8% dimethoxymethane selectivity. Dimethoxymethane could be synthesized via methoxy groups decomposed from dimethyl ether through the synergistic effect between the acid sites and the redox sites of Cs modified H3PW12O40(40%)/SiO2.

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Study of Methanol Conversion over Fe-Zn-Zr Catalyst Xiaoming Ni;Yisheng Tan;Yizhuo Han* 2007, 16(3): 326-328.  DOI: 摘要 ( 9866 )   PDF   The methanol conversion over Fe-Zn-Zr catalyst was studied at 0.1 MPa and 280−360 ℃. The experimental results indicate that the main products of methanol conversion are methane and butane, and that other hydrocarbons are scarcely produced. All results show that propylene is most probably the olefin formed first in methanol conversion rather than ethene over Fe-Zn-Zr catalyst. Methane is formed from methoxy group, and C4 is possibly yielded on the surface from propylene through binding with a methoxy group.