Liquid-Phase Cyclohexene Epoxidation with H 2 O 2 over RuO 2 -Loaded Mesoporous-Assembled TiO 2 Nanocrystals: Catalyst P
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Liquid-Phase Cyclohexene Epoxidation with H2O2 over RuO2-Loaded Mesoporous-Assembled TiO2 Nanocrystals: Catalyst Preparation and Recyclability Kittisak Woragamon • Siriporn Jongpatiwut Thammanoon Sreethawong
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Received: 8 January 2010 / Accepted: 26 February 2010 / Published online: 17 March 2010 Ó Springer Science+Business Media, LLC 2010
Abstract The purpose of this work was to investigate the liquid-phase cyclohexene epoxidation with H2O2 using RuO2-loaded mesoporous-assembled TiO2 nanocrystals. The loading of RuO2 on the mesoporous-assembled TiO2 was performed by two methods: (1) incipient wetness impregnation (IWI) (RuO2/TiO2 (IWI)) and (2) single-step sol–gel (SSSG) (RuO2/TiO2 (SSSG)). Among the investigated RuO2/TiO2 (IWI) and RuO2/TiO2 (SSSG) catalysts, 1 mol.% RuO2/TiO2 (SSSG) calcined at 450 °C was found to possess relatively high catalytic performance based on the cyclohexene conversion and cyclohexene oxide selectivity. The recyclability of the RuO2/TiO2 (IWI) and RuO2/ TiO2 (SSSG) catalysts was also investigated. It was found that after three consecutive catalytic reaction cycles, the RuO2/TiO2 (IWI) exhibited a slight decrease in cyclohexene conversion, but a significant decrease in cyclohexene oxide selectivity. On the other hand, the RuO2/TiO2 (SSSG) exhibited almost unchanged conversion and cyclohexene oxide selectivity, indicating its much higher stability. XRF and TPR results indicate that the high stability of the RuO2/TiO2 (SSSG) is due to the strong metal oxide-support interaction.
K. Woragamon S. Jongpatiwut (&) T. Sreethawong (&) The Petroleum and Petrochemical College, Chulalongkorn University, Soi Chula 12, Phyathai Road, Pathumwan, Bangkok 10330, Thailand e-mail: [email protected] T. Sreethawong e-mail: [email protected] S. Jongpatiwut T. Sreethawong Center for Petroleum, Petrochemicals, and Advanced Materials, Chulalongkorn University, Bangkok 10330, Thailand
Keywords Cyclohexene epoxidation RuO2/TiO2 Mesoporosity Incipient wetness impregnation Single-step sol–gel Recyclability TPR XRF
1 Introduction Recently, olefin epoxidation has become one of the most important reactions in organic synthesis for the finechemical industry. Through an oxygen transfer reaction, the epoxidation of olefins—such as ethylene, propylene, cyclohexene, etc.—leads to the formation of oxygenated molecules, the so-called epoxides [1], which are very valuable and versatile intermediates for many industrial purposes. Particularly, cyclohexene oxide is an important organic intermediate since its market demand has been steadily increasing over recent years for the production of pharmaceuticals, plant-protection agents, pesticides, and stabilizers for chlorinated hydrocarbons [2]. In the cyclohexene epoxidation, a peroxy acid is normally employed as the oxidant for attaining the transformation of cyclohexene to cyclohexene oxide as it possesses an oxygen–oxygen bond, which behaves as a source of electrophilic oxygen when reacting with the cyclohexene molecule [3–5]. Even though the
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