Enhanced Stability of HZSM-5 Supported Ga 2 O 3 Catalyst in Propane Dehydrogenation by Dealumination
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Enhanced Stability of HZSM-5 Supported Ga2O3 Catalyst in Propane Dehydrogenation by Dealumination Bingjun Xu Æ Tao Li Æ Bo Zheng Æ Weiming Hua Æ Yinghong Yue Æ Zi Gao
Received: 26 May 2007 / Accepted: 30 July 2007 / Published online: 22 August 2007 Ó Springer Science+Business Media, LLC 2007
Abstract Gallium oxide catalysts supported on HZSM-5 with different Si/Al ratios were characterized by pyridine adsorption FT-IR, model reactions and XPS studies. As the Si/Al ratio of the support HZSM-5 zeolite rises, the acidity of the supported catalysts decreases accordingly, which comes from two aspects: the loss of acid sites present on HZSM-5 support and the loss of the acid sites present on gallium oxides. The latter was caused by the change in the interaction between Ga2O3 and support. The initial activity in the propane dehydrogenation decreases with increasing Si/Al ratio while the stability increases. The enhanced stability is thought to be caused by the decrease of the acidity of the catalysts, resulting in the suppression of the side reactions, such as cracking and oligomerization. Keywords Ga2O3/HZSM-5 Propane Dehydrogenation Acidity Stability
1 Introduction The process of catalytic dehydrogenation of propane into propene is of increasing interest since the production propene from steam cracking and FCC is not sufficient to meet the increasing needs of the market. Dehydrogenation of propane is an endothermic reaction which requires relatively high temperature to obtain high yield of propene. Thermal cracking side reactions are favoured at high temperature, leading to a decrease in product yield and an
B. Xu T. Li B. Zheng W. Hua Y. Yue (&) Z. Gao Department of Chemistry and Shanghai Key Laboratory of Molecular Catalysis and Innovative Materials, Fudan University, Shanghai 200433, P.R. China e-mail: [email protected]
increase in catalyst deactivation. The oxidative dehydrogenation of alkanes by carbon dioxide has been proposed as an alternative. Rather high selectivity towards propene has been reported over some catalysts, such as rare earth vanadates [1], supported Cr2O3 [2], and Ga2O3 [3, 4]. And it has been found that carbon dioxide can markedly promote the dehydrogenation of ethane and propane over gallium oxide catalysts [5]. However, no agreement on the main role of carbon dioxide in reaction has been reached yet. Nakagawa et al. proposed CO2 promoted desorption of olefin products from the catalyst surface [6], and Michorzyk et al. considered CO2 consumed hydrogen via reverse water gas shift reaction [4]. In our previous work it was found that the reverse water gas shift reaction and the Boudouard reaction of CO2 may account for the enhanced catalytic activity and stability over Ga2O3 catalysts [3]. Besides, the stability of these catalysts is still rather poor and the activity declined dramatically with the reaction time, which is fatal for industrial application [1–4]. Aromatization of light paraffins over Ga-promoted HZSM-5 catalysts has been studied intensely in the previous decade.
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