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2003, Vol. 12, No. 3　Online: 2003-09-30

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A Review on Complete Oxidation of Methane at Low Temperatures Zhenhua Li;Gar B. Hound 2003, 12 (3): 153-160.  摘要 ( 10158 )   PDF(282KB) ( 3691 )   This paper reviews recent developments in complete oxidation of methane at low temperatures over noble metal catalysts in the past 20 years. The Pd/Al2O3 catalyst system is fully discussed. The review mainly focuses on the kinetic aspects of methane oxidation over this catalyst, and methane activation behavior over Pd and PdO phases (the form of PdO on the surface, transient behavior, the nature of the active sites, the in uence of metal particle size and their structure sensitivities, and so on). Some Pd catalysts supported on other oxides besides the Al2O3 support are brie y discussed. Possible routes of non-noble metal catalysts as substitutes for the Pd catalyst are also proposed.

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Preliminary Synthesis and Characterization of Mesoporous Nanocrystalline Zirconia Xinmei Liu;Gaoqing Lu;Zifeng Yan 2003, 12 (3): 161-166.  摘要 ( 7956 )   PDF(489KB) ( 1942 )   A novel method to prepare mesoporous nano-zirconia was developed. The synthesis was carried out in the presence of PEO surfactants via a solid-state reaction. The materials exhibit a strong diraction peak at low 2 angle and their nitrogen adsorption/desorption isotherms are typical of type IV with H1 hysteresis loops. The pore structure imaged by TEM can be described as wormhole domains. The tetragonal zirconia nanocrystals are uniform in size (around 1.5 nm) and their mesopores focus on around 4.6 nm. The zirconia nanocrystal growth is tentatively postulated to be the result of an aggregation mechanism. This study also reveals that the PEO surfactants can interact with the Zr-O-Zr framework to reinforce the thermal stability of zirconia. The ratio of NaOH to ZrOCl2, crystallization and calcination temperature play an important role in the synthesis of mesoporous nano-zirconia.

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CO2 Reforming of CH4 over Ni/CeO2-ZrO2-Al2O3 Prepared by Hydrothermal Synthesis Method Chunlin Li;Yilu Fu;Guozhu Bian;Tiandou Hu;Yaning Xie;Jing Zhan 2003, 12 (3): 167-177.  摘要 ( 9824 )   PDF(550KB) ( 2329 )   The Ni/CeO2-ZrO2-Al2O3 catalyst with dierent Al2O3 and NiO contents were prepared by hydrothermal synthesis method. The catalytic performance for CO2 reforming of CH4 reaction, the interaction among components and the relation between Ni content and catalyst surface basicity were investigated. Results show that the interaction between NiO and Al2O3 is stronger than that between NiO and CeO2-ZrO2. The addition of Al2O3 can prevent the formation of large metallic Ni ensembles, increase the dispersion of Ni, and improve catalytic activity, but excess Al2O3 causes the catalyst to deactivate easily. The interaction between NiO and CeO2 results in more facile reduction of surface CeO2. The existence of a small amount of metallic Ni can increase the number of basic sites. As metallic Ni may preferentially reside on the strong basic sites, increasing Ni content can weaken the catalyst basicity.

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Conversion of Methane to C2 Hydrocarbons via Cold Plasma Reaction Baowei Wang;Genhui Xu 2003, 12 (3): 178-182.  摘要 ( 7604 )   PDF(297KB) ( 2373 )   Abstract: Direct conversion of methane to C2 hydrocarbons via cold plasma reaction with catalysts has been studied at room temperature and atmospheric pressure. Methane can be converted into C2 hydrocarbons in dierent selectivity depending on the form of the reactor, power of plasma, ow rate of methane, ratio of N2/CH4 and nature of the catalysts. The selectivity to C2 hydrocarbons can reach as high as 98.64%, and the conversion of methane as high as 60% and the yield of C2 hydrocarbons as high as 50% are obtained. Coking can be minimized under the conditions of: proper selection of the catalysts, appropriate high ow rate of inlet methane and suitable ratio of N2 to CH4. The catalyst surface provides active sites for radical recombination.

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Methane Decomposition over Ni/α-Al2O3 Promoted by La2O3 and CeO2 Pengbo Jiang;Yongchen Shang;Tiexin Cheng;Yingli Bi;Keying Shi;Shuquan Wei;Guolin Xu;Kaiji Zhen 2003, 12 (3): 183-188.  摘要 ( 7884 )   PDF(363KB) ( 2163 )   The decomposition of methane on Ni/a-Al2O3 modified by La2O3 and CeO2 with different contents has been investigated and the ralationship between methane decomposition and removal of carbon by CO2 over these catalyst has also been studied by pulse-chromatography. The catalysts were characterized by TPR and XRD. It was shown that Ni/a-Al2O3 could be promoted by adding La2O3, and the carbon species produced over this catalyst was activated and eliminated by CO2. But CeO2 would suppress the decomposition of methane over Ni crystallite. Both La2O3 and CeO2 can inhibit aggregation of the Ni particles. Decomposition of methane over the Ni-based catalysts is structure sensitive to a certain extent.

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Kinetics of Carbon Deposition on Hexaaluminate LaNiAl11O19 Catalyst During CO2 Reforming of Methane Zhanlin Xu;Shuyong Jia;Lina Zhao;Yurong Ren;Yan Liu;Yingli Bi;Kaiji Zhen 2003, 12 (3): 189-194.  摘要 ( 8938 )   PDF(363KB) ( 2125 )   In this paper, the properties of carbon deposited on hexaaluminate LaNiAl11O19 catalyst were characterized by X-ray photoelectron spectroscopy (XPS), and in the meantime, the amount of carbon deposited on the catalyst, after both CH4 decomposition and CO2 reforming of CH4, was de- termined by means of thermogravimetric analysis (TGA), respectively. The rates of carbon deposited on the catalyst were also investigated and the apparent kinetic equation of CO2 reforming of CH4: vc = kp0:72(CH4)p-0.55(CO2), established by analyzing the relation between the rates of deposited carbon and the pressure ratio of CH4 and CO2.

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Enhancement in Activity of a Vanadium Catalyst for the Oxidation of Sulfur Dioxide by Radio Frequency Plasma During the Preparation Process Zhenxing Chen;Honggui Li;Lingsen Wang 2003, 12 (3): 195-200.  摘要 ( 8609 )   PDF(340KB) ( 2020 )   Radio frequency plasma was used to prepare a vanadium catalyst. The results showed that activating time of the catalyst could be shortened quickly and the catalytic activity was improved to some extent with the use of plasma. Catalyst Ls-9 was prepared under an optimal condition of 40 W discharge power, 10 min discharge time and 8 Pa gas pressure. The catalytic activity was up to 54.7% at 410oC, which was 2.2% higher than that of the Ls-8 catalyst. Only 10 min was needed to activate the catalyst with plasma, which was 1/9 of the traditional calcination time. For Ls-9, both the endothermic as well as the exothermic peaks detected by dierential thermal analysis shifted to higher temperatures obviously, indicating that its crystal phase could melt easily. There existed an apparent endothermic peak at 283oC. SEM photographs showed a uniform size distribution. It is inferred that the quadrivalent vanadium compound may exist mainly in the form of VOSO4.

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Study on the Kinetics of the Catalytic Reforming Reaction of CH4 with CO2: Determination of the Reaction Order Chunyang Ji;Lihong Gong;Jiawei Zhang;Keying Shi 2003, 12 (3): 201-204.  摘要 ( 7531 )   PDF(279KB) ( 2368 )   The kinetics of the catalytic reforming reaction of methane with carbon dioxide to produce synthesis gas on a Ni/a-Al2O3 and a HSD-2 type commercial catalyst has been studied. The results indicate that the reaction orders are one and zero for methane and carbon dioxide, respectively, when the carbon dioxide partial pressure was about 12.5-30.0 kPa and the temperature was at 1123-1173 K. However, when the carbon dioxide partial pressure was changed to 30.0-45.0 kPa under the same temperature range of 1123-1173 K, the reaction orders of methane and carbon dioxide are one. Furthermore, average rate constants at dierent temperatures were determined.

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Effect of Ni Loading and Reaction Conditions on Partial Oxidation of Methane to Syngas Haitao Wang;Zhenhua Li;Shuxun Tian 2003, 12 (3): 205-209.  摘要 ( 6714 )   PDF(391KB) ( 2051 )   The partial oxidation of methane to synthesis gas is studied in this paper over Ni/Al2O3 catalysts under atmospheric pressure. The eects of Ni loading on the activity and stability of catalysts with 5 mm a-Al2O3 and r-Al2O3 pellets as supports were measured in a continuous fixed bed reactor. It is found that the optimum Ni loading is 10%. And the eect of reaction conditions on partial oxidation of methane is also studied. The methane conversion and CO selectivity increase with the increase of the reaction temperature and the space velocity on 10%Ni/a-Al2O3 catalysts. The best CH4/O2 mole ratio is 2 for CO selectivity, and the optimum space velocity is 5.4.105 h-1.