Preparation and Characterization of Ru/Al 2 O 3 /Cordierite Monolithic Catalysts for Selective Hydrogenation of Benzene
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Preparation and Characterization of Ru/Al2O3/Cordierite Monolithic Catalysts for Selective Hydrogenation of Benzene to Cyclohexene Yujun Zhao Æ Jin Zhou Æ Jianguo Zhang Æ Shudong Wang
Received: 31 January 2009 / Accepted: 8 May 2009 / Published online: 22 May 2009 Ó Springer Science+Business Media, LLC 2009
Abstract A series of Ru/Al2O3/cordierite monolithic catalysts were prepared and characterized by BET, XRD, TPR, TEM and SEM-EDAX. The catalytic performances in selective hydrogenation of benzene to cyclohexene were investigated in a continuous fixed-bed reactor. The preparation conditions significantly influence morphology, particle size, and surface area of the catalyst, subsequently affecting the catalytic performances. It was found that higher calcination temperature of the Ru-based monolithic catalyst led to the conglomeration and crystallite growth of the t-RuO2, which will decrease the catalytic activity. The lower thickness and the larger pore size of the alumina washcoating layer are the preferential choices to obtain higher cyclohexene selectivity due to the improved internal mass transfer of cyclohexene. It was also found that high ruthenium loading resulted in deep hydrogenation of cyclohexene. Moreover, the reduction temperature was optimized to 473 K and excess high temperature led to the deterioration of both activity and cyclohexene selectivity. Keywords Ruthenium Benzene Cyclohexene Hydrogenation Cordierite monolith
Y. Zhao (&) Key Laboratory for Green Chemical Technology of Ministry of Education, School of Chemical Engineering & Technology, Tianjin University, 300072 Tianjin, China e-mail: [email protected]; [email protected] Y. Zhao J. Zhou J. Zhang S. Wang (&) Modern Chemical Laboratory, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, 116023 Dalian, Liaoning, China e-mail: [email protected]
1 Introduction As an alternative process for the production of polyamides [1, 2], recently, selective hydrogenation of benzene to cyclohexene (SHBC) has draw much attention due to its atom economic, simplexes and low pollution [3, 4]. Ruthenium based catalyst, as one of the candidate for SHBC, has been investigated widely and some interesting results have been reported [5–10]. Asahi’s catalyst, which was consisted of ruthenium and zinc nano-powders (\10 nm) in a slurry system [11], is the only catalyst applied successfully in SHBC till now. The hydrogenation reaction was conducted in a tetra-phase reactor with the presence of an aqueous solution of ZnSO4, which is crucial to increase cyclohexene selectivity. The reasons could be attributed to the partially occupancy of the strong active sites by ZnSO4 and the enhanced hydrophilicity of the catalyst. A stagnant water layer on the catalyst surface will displace the adsorbed cyclohexene and benefit the leaving of cyclohexene from catalyst surface to the bulk oil phase due to its lower solubility in water. Thus the consecutive hydrogenation of cyclohexene was inhibited and higher cyclohexene yield was achieved [4, 12]. Alth
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