Methane Aromatization over Cobalt and Gallium -Impregnated HZSM-5 Catalysts
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Methane Aromatization over Cobalt and Gallium -Impregnated HZSM-5 Catalysts Jun-Feng Liu Æ Ling Jin Æ Yuan Liu Æ Yun-Shi QI
Received: 24 December 2007 / Accepted: 13 March 2008 / Published online: 13 September 2008 Ó Springer Science+Business Media, LLC 2008
Abstract The influence of the catalyst acidity, the ratio of cobalt in the catalyst on the conversion of methane and the stability were evaluated using a fixed-bed microreactor at atmospheric pressure and at a flow rate of 1500 mL/g h (GHSV 600 h-1). The reaction was conducted at 973 K and 1023 K over gallium and cobalt -impregnated HZSM-5 catalysts. The 2%Ga–2% Co/HZSM-5 catalyst exhibited remarkable stability with no significant deactivation for 100 h on stream, and yielded a maximum conversion of methane to benzene equal to 9.9%. These catalysts were thoroughly characterized using XRD, N2 adsorption measurements, TPD of NH3 and FT-IR. The acidity changes severely affected aromatization, and resulted in drastic modifications in product distribution. From this work, we found that only a small fraction of tetrahedral framework aluminum, which corresponds to the Bronsted acid sites, is sufficient to accomplish the aromatization of the intermediates in methane aromatization reaction, while the superfluous strong Bronsted acid sites, which can be decreased by adding Ga and Co, are shown to be related with the aromatic carbonaceous deposits on the catalysts. After adding Ga and Co the strength of Lewis acid sites of the catalyst increased. But the total amount of the acidity on the catalyst decreased.
J.-F. Liu (&) L. Jin Y. Liu Department of Chemical Engineering, Hunan University of Science & Technology, Xiangtan City, Hunan 411201, P.R. China e-mail: [email protected] Y.-S. QI Institute of Industrial Catalysis, East China University of Science and Technology, Shanghai 200237, P.R. China
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Keywords Methane Cobalt Gallium HZSM-5 Aromatization
1 Introduction It is more important to develop production of aromatic hydrocarbon by the exploitation of new raw material and technology along with the augment of demanded amount for aromatic hydrocarbon. Zeolite catalyst shows high activity for the aromatization of hydrocarbon. The production of aromatic hydrocarbon from low molecular weight alkyl hydrocarbon has developed rapidly since the Cyclar technics for the aromatization of alkyl hydrocarbon has been used. V. Kanazirev, who was the first researcher discussed the acidic and catalytic characters of Ga modified HZSM-5 zeolites [1]. Hereafter, the character of the catalyst has been researched and improved, so the productivity of aromatic hydrocarbon has increased and scope of raw material has been extended. Natural gas (mostly methane) reserves are abundant throughout the world and are becoming a promising energy source due to the increasing prices of oil. Recently, a major limitation to the utilization of the resource is the high price to transport the natural gas to the desired location. Therefore, one of the current challenges of the petrochemical ind
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