Gold supported on titanium-based metal oxides can assist the selective partial oxidation of propylene at temperatures from 313 K to 573 K in a gas containing both H2 and O2. The preparation method was found to be crucial in controlling the selectivities. In general, impregnation and chemical vapor deposition methods do not produce selective catalysts. Only the deposition-precipitation method makes gold selective to propylene oxide or propanal, suggesting that a strong contact between the gold particles and the titanium ion sites on the support is important. The effect of changing the support was also dramatic, the use of the anatase form of TiO2 and Ti-MCM-41 results in propylene oxide production, while the rutile structure of TiO2 caused complete oxidation to CO2. Microporous crystalline titanium silicates such as TS-1, TS-2, and Ti-β zeolite make gold relatively selective to propanal and of the three TS-1 gives the highest selectivity. These results indicate that the oxidation of propylene in the copresence of H2 must involve the surface of the supports and that the reaction takes place at the interface perimeter around the gold particles.
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