Functionalized Poly(ethylene glycol)-Stabilized Palladium Nanoparticles as an Efficient Catalyst for Aerobic Oxidation o
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Functionalized Poly(ethylene glycol)-Stabilized Palladium Nanoparticles as an Efficient Catalyst for Aerobic Oxidation of Alcohols in Supercritical Carbon Dioxide/Poly(ethylene glycol) Biphasic Solvent System Xiangrui Wang Æ Hanmin Yang Æ Bo Feng Æ Zhenshan Hou Æ Yu Hu Æ Yunxiang Qiao Æ Huan Li Æ Xiuge Zhao Received: 10 April 2009 / Accepted: 25 May 2009 / Published online: 10 June 2009 Ó Springer Science+Business Media, LLC 2009
Abstract The functionalized Poly(ethylene glycol) (PEG)stabilized Pd(0) nanoparticles have been utilized to selectively oxidize alcohols to the corresponding aldehydes or ketones in supercritical carbon dioxide (scCO2)/PEG (PEG-2000) biphasic system. It was demonstrated that the Pd(0) nanocatalyst was more active and selective, in comparison with the commercially available Pd/C catalyst, PVP-stabilized Pd nanocatalyst and Pd(0) catalyst without stabilization. The effects of CO2 pressure, reaction time and temperature on activity and selectivity were also further investigated in detail. The scCO2/PEG biphasic system was proved to be not only cheap and clean, but also recyclable for the aerobic oxidation of alcohols. Keywords Poly(ethylene glycol) Supercritical carbon dioxide Alcohol oxidation Palladium nanoparticles
1 Introduction The selective oxidation of alcohols into the corresponding aldehydes or ketones is a class of transformation for the
X. Wang B. Feng Z. Hou (&) Y. Hu Y. Qiao H. Li X. Zhao Key Laboratory for Advanced Materials, Research Institute of Industrial Catalysis, East China University of Science and Technology, 200237 Shanghai, China e-mail: [email protected] H. Yang Key Laboratory of Catalysis and Materials Science of the State Ethnic Affairs Commission & Ministry of Education, South-Central University for Nationalities, 430074 Wuhan, Hubei Province, China
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production of a large variety of important intermediates and fine chemical products [1], and numerous approaches have been explored successfully [2, 3]. Generally, oxidation processes based on the use of stoichiometric or excess amounts of oxidants have suffered from the disadvantage of producing much toxic waste such as chromium(VI) and manganese(IV) compounds, thus causing serious environmental problems [1, 4]. The development of clean and efficient oxidation methods for fine chemicals synthesis is a major goal of green chemistry. This has resulted in much attention being recently directed toward the development of new protocols for the aerobic oxidation of alcohols using transition-metal catalysts. Among them, palladium-based catalysts show promising catalytic activity, and different types of palladium-based homogeneous [5–7] and heterogeneous catalysts [8–10] in the form of metal complexes or nanoparticles have been reported. Poly(ethylene glycol) (PEG) is an inexpensive, nonvolatile and environmentally benign solvent, whereas the utilization of PEG as reaction media has attracted much attention [11, 12]. Supercritical carbon dioxide (scCO2, Tc = 31.0 °C, Pc = 7.4 MPa) combines liquid
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