Selective oxidation of propylene over gold deposited on titanium-based oxides

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.