Preparation and characterization of Cu/SiO2 catalyst by co-gelation process

Cu/SiO2 catalyst with bimodal pore structure was prepared by co-gelation reactions of tetramethoxysilane (TMOS) and copper nitrate in the presence of poly (ethylene oxide) (PEO) with an average molecular weight of 10,000 and the catalyst of acetic acid. In this process, the interconnected macroporous morphology was formed when transitional structures of spinodal decomposition were frozen by the sol–gel transition of silica. The addition of copper into the silica–PEO system had a negligible effect on the morphology formation. In gel formation, it was found that the crystallite sizes of the CuO estimated from the peak width in the Cu/SiO2 with the presence of PEO were not small as expected. It was considered that there was no obvious interaction between the Cu cation and PEO, most of the copper ions in wet silica gel were present in the outer solution. They easily aggregated as copper salts in the drying process of wet gel and decomposed into CuO particles in heating. While in the Cu/SiO2 with the absence of PEO, the Cu was selectively entrapped as small particles in the gel skeleton due to the interaction between Cu aqua complex and silica gel network.