Trimetallic Au/Pt/Rh Nanoparticles as Highly Active Catalysts for Aerobic Glucose Oxidation
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INTRODUCTION
IN recent years, considerable research efforts have been made to achieve the colloidal dispersion of small metal nanoparticles (NPs) in a homogeneous solution.[1] Such metal NPs can act as excellent homogeneous catalysts for many organic reactions. For instance, colloidal silver catalysts showed better catalytic properties than a commercial silver catalyst in the oxidation of ethylene,[2] high conversion and selectivity for the hydrogenation of cyclohexene were achieved with Pt and Pd sols,[3] and enantioselective reductions of o-cresol derivates were performed well with colloidal rhodium stabilized and modified by chiral amines.[4] Bimetallic catalysts have been extensively investigated aiming to improve the quality of the catalyst. The effect of the second added metals in them can be explained in terms of an ensemble and/or a ligand effect.[5] For example, Au/Pd colloids are efficient catalysts for aerobic glucose oxidation [6]; Cu/Pd bimetallic colloids display a high catalytic activity and selectivity for hydration of acrylonitrile to acrylamide.[7] Trimetallic nanoparticles (TNPs) are also important in catalysis because of the synergic interaction between three different metallic elements contained in one particle, which
HAIJUN ZHANG and SHAOWEI ZHANG, Professors, and YINGNAN CAO, Master Student, are with the of The State Key Laboratory of Refractories and Metallurgy, Wuhan University of Science and Technology, Wuhan 430081, P.R. China. Contact e-mail: [email protected] LILIN LU, Lecturer, is with the College of Chemical Engineering and Technology, Wuhan University of Science and Technology, Wuhan 430081, P.R. China. ZHONG CHENG, Lecturer, is with the College of Chemistry and Molecular Sciences, Wuhan University, Wuhan, 430072, P.R. China. Manuscript submitted April 27, 2014. Article published online October 21, 2014. METALLURGICAL AND MATERIALS TRANSACTIONS B
leads to enhanced catalytic activity and selectivity which are distinct from those of the corresponding monometallic nanoparticles (MNPs) or bimetallic nanoparticles (BNPs).[8–14] Another major reason for the interest in TNPs is because that their chemical and physical properties could be tuned by varying the size, composition, and extent of mixing, and thus some novel properties different with those of MNPs or BNPs obtained. There have been limited reports but rapidly growing interest in TNPs in the last few years.[15] Toshima’s group developed polymer-protected Pd/Ag/ Rh triple-layered core–shell TNPs by mixing dispersions of polymer-protected Rh NPs and Pd@Ag core–shell BNPs. The spontaneously formed TNPs having an atomic composition of Pd/Ag/Rh = 1/2/13.5 and an average diameter of 2.2 nm showed the highest catalytic activity among all the metal NP catalysts for hydrogenation of methyl acrylate at 303 K (30 °C) in a hydrogen atmosphere.[16] Zhou et al. prepared onion-like Pd-BiAu/C catalyst particles with an average diameter of 13 nm, which were composed of high content of Au inner core, Bi-rich intermediate layer, and Pd-rich external l
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