Bimetallic PdCu Nanoparticle Catalyst Supported on Hydrotalcite for Selective Aerobic Oxidation of Benzyl Alcohol
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Bimetallic PdCu Nanoparticle Catalyst Supported on Hydrotalcite for Selective Aerobic Oxidation of Benzyl Alcohol Shun Nishimura,1 Nao Yoshida1 and Kohki Ebitani1,* 1 School of Materials Science, Japan Advanced Institute of Science and Technology, 1-1 Asahidai, Nomi, Ishikawa 923-1292, Japan. ABSTRACT To decrease the amount of precious metal usage for Pd-catalyzed aerobic alcohol oxidation, various amount of Cu-contained Pd bimetallic nanoparticle-supported solid base hydrotalcite catalyst (PdxCuy-PVP/HTs) were prepared and applied for aerobic benzyl alcohol oxidation. It was found that the addition of Cu atoms into Pd in the range of 0-40% provided a similar or a little superior activity to that of Pd100-PVP catalyst, whereas a large quantity of coexistence Cu (>40%) gradually decreased their activity of the catalyst. The aerobic benzyl alcohol oxidation over Pd80Cu20-PVP/HT served 77% yield and 95% selectivity towards benzaldehyde at 313 K for 5 h in toluene under O2 flow. X-ray adsorption spectroscopy (XAS) studies and scanning transmission electron microscopy-high angle annuar dark field (STEMHAADF) with energy dispersive X-ray spectroscopy (EDS) analyses suggested that Cu atoms doping into Pd(0) NP influenced not only localized nanostructure but also oxidation state around Pd atoms. We suggested that substitution of precious metal with small amount of transition metals such as Cu lead to geometric/electronic changes in active sites would be one of nice strategies for reducing the cost for the catalyst in the oxidation process. INTRODUCTION Selective oxidation of alcohols is one of the important industrial reactions for fine chemicals production; it serves key intermediates such as aldehydes, ketones and carboxylic acids. Stoichiometric oxidation processes using homogeneous oxidants such as KMnO4, K2Cr2O7 and TEMPO or metal-complex catalyzed oxidation process [1,2] have a long history for the oxidation reactions. However, these conventional processes have serious disadvantages derived from salts formation, catalyst separation and purification after product formation. For building more environmentally-friendly chemical process, heterogeneous catalytic systems for aerobic alcohol oxidation have been studied by several groups [3,4]; it provides only water as co-product after reaction in theory, and the catalyst was easily separated from the reaction mixture. Especially in this area, precious metals (i.e. Au, Pd, Pt, Ru etc) based catalysts have been studied widely for the oxidation reaction [5], however, utilization of the precious metal needs to be minimized in order to replace these precious catalysts for the classical process in industrial plant scales. In this study, we focused on the transition metal Cu incorporated Pd catalyst. The PdCu bimetallic catalyst has been widely applied for hydration of acrylonitrile to acrylamide, hydrogenation of 1,3-cyclooctadiene, Sonogashira cross-coupling, CO oxidation, NO reduction and so on [6-9]. Because the nanohybrid materials composed with transition metal and precious m
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