Photo-catalysis of ethane and carbon dioxide to produce hydrocarbon oxygenates over ZnO-TiO2/SiO2 catalyst

The supported n-p coupled semiconductor materials ZnO-TiO2/SiO2 were prepared using the method of modifying the silica surface character. The chemical structure, photoabsorbing behaviors and chemisorbing properties of the catalysts were characterized by IR spectra, Raman spectra, UV-vis reflectance spectra and TPD-MS experiments. It was shown that the Zn-O-Ti bonds have been formed on the surface of ZnO-TiO2/SiO2 catalyst. The addition of ZnO extends the photo absorption range of TiO2/SiO2 sample through the formation of Zn-O-Ti bond. CO, and ethane can be chemisorbed on the surface of ZnO-TiO2/SiO2 catalyst and desorbs at 388 and 428 K, respectively. Under UV irradiation, CO, chemisorption state can undergo discomposing process to form CO at 465 K, and a new ethane adsorption state was formed at around 500 K. Photo-oxidation of ethane using carbon dioxide can mainly produce propanal, ethanol, acetaldehyde in the temperature range of 393-493 K. The presence of ZnO improved the catalytic activity and promoted the formation of hydrocarbon oxygenates. The propanal yield of 75.6 mumol h(-1) and ethanol yield of 50.9 mumol h(-1) can be obtained over 5% ZnO-TiO2/SiO2 catalyst at 473 K. Reacting temperature has significant effects on the product yields. The temperature of 473 K will be preferable for the selective formation of propanal and ethanol. (C) 2004 Elsevier B.V. All rights reserved.