Experimental section Zn(Ac) 2 •2H 2 O was purchased from Tianjing Kermel Chemical Reagent Co., Ltd., and was used as received without further purification. The preparation of ZnO is very simple. The evaporating dish with 28g of Zn(Ac) 2 •2H 2 O solid was placed into a muffle furnace, for which the temperature was increased from room temperature to 600 degree with a heating rate of 5 min -1 in an air atmosphere and kept at the maximum temperature for 120 min. After naturally cooling to room

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... rature, the white powder was collected. The sample was denoted as ZnO-600, where 600 refer to the temperature. The quality of ZnO is about 9.9g, corresponding to the higher yield of 97%. Both the production and yield of this solid phase route are much higher than that of solution-based methods. To study the effect of temperature on the microstructure and performance, ZnO-400, ZnO-800 and ZnO-900 catalysts were also prepared . Characterization Transmission electron microscopy (TEM, JEOL-2010) with an acceleration voltage of 200 kV was used to characterize the morphology of samples. X-ray powder diffraction (XRD) was performed with a Rigaku (Japan) D/MAX-rA X-ray diffractionmeter equipped with graphite monochromatized Cu Kα radiation (γ=1.541874 Å). Fourier transform infrared (FT-IR) spectra were carried out on NICOLETiS10 FT-IR spectrometer. X-ray photoemission spectroscopy (XPS) studies were carried out on a Kratos-AXIS UL TRA DLD with Al Kα radiation source. The nitrogen adsorption/desorption isotherms were measured at 77 K using a Electronic Supplementary Material (ESI) for Chemical Communications This journal is