Highly active and sintering-resistant heteroepitaxy of Au nanoparticles on ZnO nanowires for CO oxidation

摘要

Gold was supported on commercial ZnO powders (P) and homemade ZnO nanowires (NWs) by a modified deposition-precipitation method.X-ray diffraction and transmission electron microscopy investigation indicated that the size of the Au nanoparticles (NPs) depended strongly on the calcination temperature.The Au NPs were highly dispersed (＜ 5nm) on both supports with calcination temperatures ＜ 400℃.However,after calcination at 600 ℃ the Au NPs aggregated much more severely on ZnO P than on ZnO NWs.Gold NPs epitaxially grew into the {10-10} facets of the ZnO NWs after calcination at temperatures ＞ 400 ℃.Such unique anchoring mechanism accounts for the much better experimentally observed sintering resistance.X-ray photoelectron spectra showed that Au existed as both metallic Au0 and Auδ+ species in all the synthesized catalysts with or without calcination treatment;the ratios of Auδ+/Au0,however,varied,depending on the treatment conditions.Catalytic tests showed that the activity for CO oxidation strongly depended on the size of the Au NPs.After calcination at 600 ℃,the specific rate for CO oxidation at room temperature decreased about 30 times on Au/ZnO P but only about 4 times on Au/ZnO NW.Stability tests demonstrated that the Au/ZnO NW catalysts had better stability for CO oxidation.