Effect of Ti-Si Mixed Oxide Support on Gold Catalysts for Gas-Phase Epoxidation of Propylene

Titania-silica mixed oxides prepared by hydrolytic and one-step non-hydrolytic sol-gel routes using TICl4 and SiCl4 as precursors were employed as the gold catalyst supports for gas-phase epoxiclation of propylene in O-2 and H-2. Characterization studies of the supports and catalysts were performed by means of X-ray diffraction, ultraviolet-visible absorption spectroscopy, N-2 adsorption, and high-resolution transmission electron microscopy. The results indicated that the amorphous Ti-Si mixed oxides containing 6%-14% of Ti could be prepared by both sol-gel routes, but those by non-hydrolytic sol-gel afforded higher surface area and significant mesopores. A superior catalytic performance was obtained with the gold catalyst supported on the non-hydrolytic sol-gel Ti-Si mixed oxide containing 10% of Ti. The propylene conversion was 5.7% at the initial 60 min and 3.3% at 240 min of time on stream. The selectivity for propylene oxide was as high as 95%. The influences of aging time for the non-hydrolytic sol-gel and pH value for the Au deposition-precipitation on the performance of the Au catalyst were also discussed.