Preparation and composition analysis of catalysts supported by CuO-CoO-MnO/SiO2 nanocomposite aerogels

摘要

Using tetraethyl orthosilicate (TEOS) as Si source, and aqueous solution of Cu, Co and Mn acetates as the precursors, CuO-CoO-MnO/SiO2 nanocomposite aerogels were prepared through different methods, such as sol-gel process, CO2 supercritical drying (SCD) technique, and ethanol SCD technique, respectively. Catalysts supported by the nanocomposite aerogels were prepared by impregnation method. They were used in the synthesis of diphenyl carbonate (DPC). The microstructures of the nanocomposite aerogels and the catalysts were observed with transmission electron microscopy (TEM). The specific surface area, pore size and pore size distribution of the nanocomposite aerogels were determined by the Brunauer-Emmett-Teller (BET) method. The compositions of the nanocomposite aerogels and the catalysts were analyzed by energy dispersive spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). The results show that nanocomposite aerogel prepared by ethanol SCD technique shows lower transition metals loss compared with that through CO2 SCD technique. The mole fraction of active transition metals in the nanocomposite aerogel prepared through ethanol SCD technique is 13.77 mol%, and that in the ultrafine particles of the nanocomposite aerogel is 67.65%. The mole fraction of active transition metals decreased to some extent after it was used as a catalyst carrier in the synthesis of DPC. The yield of DPC catalyzed by the novel supported catalyst is 26.31 mass%, which is much higher than other porous carriers, such as SiO2 xerogels, SiO2 aerogels, CuO/SiO2 composite xerogels, CuO/SiO2 composite aerogels and CuO-CoO-MnO/SiO2 composite xerogels synthesized in this study.