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2004, Vol. 13, No. 3　Online: 2004-09-30

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Some problems in adsorption and calorimetric studies of the steps of catalytic processes Victor E. Ostrovskii 2004, 13 (3): 123-147.  摘要 ( 7520 )   PDF(816KB) ( 2536 )   Abstract: Principal side factors as well as technical and procedural peculiarities capable of distorting the results of measurements of adsorbed and desorbed amounts, of falsifying the nature of the processes proceeding in the systems under study, and of promoting artifacts in calorimetric and other studies of gas chemisorption on powders are considered. Modified techniques and procedures allowing the elimination of sources of side phenomena and artifacts and freeing traditional glass static adsorption apparatuses and experimental procedures from undesirable factors and peculiarities are proposed. Some available chemisorption and calorimetric data representing artifacts and also some data that are not artifacts but, due to imperfections of chemisorption techniques, show up as artifacts are presented and discussed. Several applications of the improved techniques and procedures to calorimetric and adsorption studies of the steps of catalytic processes proceeding on the basis of natural gas and of products of its processing are presented and discussed.

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Improved Performance of W/HZSM-5 Catalysts for Dehydroaromatization of Methane Nor Aishah Saidina Amin;Kusmiyati 2004, 13 (3): 148-159.  摘要 ( 10088 )   PDF(469KB) ( 1722 )   Abstract: The dehydroaramatization of methane over W-supported ZSM-5 with varying degrees of Li+ ion-exchanged catalysts was studied with and without oxygen at 1073 K and atmospheric pressure. Catalyst activity and stability were found to be influenced by the catalyst acidity related to Bronsted acid sites and by the presence of oxygen in the feed. The NH3-TPD and FTIR-pyridine results demonstrated that partially exchanged of H+ ions by Li+ into the W/HZSM-5 catalysts could be used to control the amount of strong acid sites on the catalyst surface. Without oxygen, the 3WHLi-Z (5:1) catalyst that has strong acid sites equal to nearly 74% of the original strong acid sites in the parent HZSM-5 exhibited the highest methane conversion and selectivity towards amatics. However, the catalyst deactivated in a five hour period. In the presence of oxygen, the catalyst activity and stability could be improved further. The results of this study revealed that a suitable amount of strong Bronsted acid sites as well as oxygen addition in the feed increased the catalyst activity and stability. The 3WHLi-Z(5:1) catalyst exhibited improved performance in the dehydroaromatization of methane.

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Effect of Dimethyl Ether Co-feed on Catalytic Performance of Methane Huiying Chen;Yonggang Li;Wenjie Shen;Yide Xu;Xinhe Bao 2004, 13 (3): 160-166.  摘要 ( 8962 )   PDF(420KB) ( 2180 )   Abstract: The effect of dimethyl ether (DME) co-feed on the catalytic performance of methane dehydroaromatization (MDA) over 6Mo/HZSM-5 catalyst was investigated as a function of DME concentration under reaction conditions of T=1023 K, p=101 kPa and SV=1500 ml/(g·h). A high benzene yield was obtained and the stability of the catalyst was improved by adding 1.5%DME to the CH4 feed. The C6H6 yield was as high as ca. 10% even after reaction for 6 h. The stability of the catalyst was further improved when DME concentration in the co-feed gas was increased to an appropriate value. TGA and TPO results of the used 6Mo/HZSM-5 catalyst showed that the amount of coke on the used catalyst was reduced and the chemical nature of the coke was changed. When 1.5%DME was added to the CH4 feed, the coke formed on the catalyst could be burned off more easily than that when only CH4 was used as reactant. It is supposed that the oxygen in DME may play a role in preventing the coke burnt off at lower temperature from transforming into the coke burnt off at higher temperature, which results in the improvement of the stability of the catalyst.

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Catalytic Performance of CeO2/ZnO Nanocatalysts on the Oxidative Coupling of Methane with Carbon Dioxide and their Fractal Features Yongjun He;Blun Yang;Haimin Pan;Guozhi Li 2004, 13 (3): 167-171.  摘要 ( 8408 )   PDF(755KB) ( 2176 )   Abstract: nanocatalysts were prepared from the coupling route of homogeneous precipitation with microemulsion and the impregnation method. The catalytic performance of these two kinds of catalysts on the oxidative coupling of methane with carbon dioxide was tested and compared; the fractal behavior of the nanocatalysts was analyzed using fractal theory. The CeO2/ZnO nanocatalysts had much higher activity than the catalysts prepared by impregnation method. There was no regular relationship between the average size of CeO2/ZnO talysts and their catalytic performance; however, the conversion of methane increased with the increase of the fractal dimension of CeO2/ZnO nanocatalysts.

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Selective Oxidation of Isobutene over CsFeCoBiMnMoOx Mixed Oxide Catalyst Zhenshan Peng;Changlin Yu;Tiejun Cai;Qian Deng 2004, 13 (3): 172-176.  摘要 ( 8867 )   PDF(326KB) ( 2048 )   Abstract: Mixed oxide catalyst Cs0.1Fe2Co6BiMnMo12Ox was prepared by the coprecipitation method. Selective oxidation of isobutene was carried out in a fixed-bed reactor over s0.1Fe2Co6BiMnMo12Ox. The results showed that the catalyst had high catalytic activity. Under the optimum reaction conditions (n(i-C4):n(O2)=1:2--1:4, space velocity=180 h –1, T=360 C, the yields of methacrolein and methacrylic acid can reach 80% and 8%, respectively. The total yield of liquid products (methacrolein, methacrylic acid and acetic acid) can reach about 90%.

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Study on the Deactivation Kinetics of Pd(PPh3)2Cl2 in the Monocarbonylation of Benzyl Chloride Zumin Qiu;Yunbing He;Huiping Xiao 2004, 13 (3): 177-183.  摘要 ( 9248 )   PDF(288KB) ( 1988 )   The deactivation kinetics of Pd(PPh3)2Cl2 in the monocarbonylation of benzyl chloride to synthesize phenylacetic acid is studied in this paper. Solid 1-(2-pyridylazo)-2-naphthol (PAN) is used as the colouring agent, and the concentration of Pd(PPh3)2Cl2 in the system is measured through absorptiometry. The result shows that the optimum condition of the chromogenic reaction between Pd2+ and PAN is: 0.5 ml of 0.04% PAN added to 10 ml of Pd2+ solution (1×10-6~2.0×10-5 mol·L-1), and heated in a constant temperature water bath at 40 ℃ for about 30 min, with pH of the solution being about 3.0. The molar coefficient of absorption is 1.384×104 L/(mol·cm); the orders of the hydrolytic reaction to the concentration of Pd(PPh3)2Cl2, PPh3, phenylacetic acid and NaOH are 0.5, minus 0.8, 2 and 1.2, respectively. The activation energy (E) of the hydrolytic reaction is 75.59 kJ/mol, and the pre-exponential factor is 1.68×1012.