The Effect of oxygen defects on Activity of Au/ZnO Catalyst in Low Temperature Oxidation of Benzyl Alcohol
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The Effect of oxygen defects on Activity of Au/ZnO Catalyst in Low Temperature Oxidation of Benzyl Alcohol R. Shidpour1,4,*, M. Vossoughi 1 ,2, and A.R. Simchi 1,3 1
Institute for Nanoscience & Nanotechnology, Sharif University of Technology, Tehran, Iran Chemical & Petroleum Engineering Department, Sharif University of Technology, Tehran, Iran Material science and engineering Department, Sharif University of Technology, Tehran, Iran 4 Department of Chemistry, University of California, Riverside, USA 2 3
Abstract: Gold nanoparticles supported on ZnO nanostructures were prepared through a simple chemical-thermal method and characterized by SEM, TEM, XRD and photo luminescence (PL) spectroscopy. Effect of annealing temperature on catalytic activity of these Au/ZnO nanocatalysts were investigated by aerobic oxidation of benzyl alcohol. The results indicated that the catalyst with ZnO nanowire support annealed at 300 oC exhibited more activity than Au/ZnO catalyst supported on ZnO nanoparticles annealed at 600 oC. The Au/ZnO-nanowire achieved to increase the benzaldehyde selectivity and yield to 93.7 % and 85.6 %, respectively, at 60 oC whereas in Au/ZnO-nanoparticle the benzaldehyde selectivity and yield to 85.1 % and 69.9 %, respectively at 80 oC. The XRD and PL spectroscopy revealed that the supports have interstitial zinc (Zni), oxygen vacancy (VO-2) defects definitely but there is no evidence for interstitial oxygen (Oi) and zinc vacancy (VZn) defects and single ionized charged oxygen vacancy (VO).
1. Introduction The oxidation of alcohols into their corresponding aldehydes and ketones is one of the most important reactions in both laboratory and industrial synthetic chemistry [1]. In recent years, the high catalytic activity of Au as a low temperature CO oxidation catalyst [2] has started intensive research in the use of Au nanoparticles for the liquid phase oxidation of alcohols [3-7]. In comparative studies of aerobic catalytic oxidation of alcohol using supported Pt, Pd, or Au as catalyst, Au has shown to have the highest selectivity and to be less prone to metal leaching, over-oxidation, and self-poisoning by strong adsorbed byproducts. Generally, the adsorption and catalytic properties of Au depend on its particle size and surface chemistry of support which the latter could be controlled by the preparation method and type of catalyst support [8̽10]. One of the most important parameters that can change the nature of support surface is the morphology since it could change the coordination number of the surface atoms. In this work, the co-precipitation method was employed in order to fabricate gold nanocatalysts with different morphologies in the support. The nanocatalysts used in aerobic oxidation of benzyl alcohol, showed unusual high activity in oxidation of benzyl alcohol. Finally, the concentration of defects were probed by optical and structural analysis to explore unusual defect structure in this ZnO support. 2. Experimental 2.1. Preparation and characterization of Au/ZnO To synthesize gold catalyst wi
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