SELECTIVE PHOTOOXIDATION OF LIGHT ALKANES USING SOLID METAL-OXIDE SEMICONDUCTORS

Activities of n-type solid metal oxide semiconductors for aerobic photo-oxidation of simple C1-C3 alkanes were examined at temperatures from ambient to ca. 550 K. Whereas the reaction with methane produced a small amount of methanal (4.7 mumol h-1) together with carbon dioxide, and selectivity for methanal was low (ca. 10%), photo-oxidation of ethane with 0.25 g of zinc oxide at 493 K produced 84 mumol h-1 of ethanal with a high selectivity of ca. 75%. The reaction with propane under similar conditions gave 57 mumol h-1 of propanal and 56 mumol h-1 of acetone with a combined selectivity of over 75% on carbon base. For these reactions UV irradiation was indispensable, and catalytic performances of zinc oxides depended greatly on their properties and preparation. The yields of the products were very small at ambient temperature, and increased with increasing temperature up to 500-550 K. The titanium oxide catalysts produced aldehydes and ketones from light alkanes, but in lower selectivities than the zinc oxide catalysts.