Photo-oxidation of light alkenes using solid metal oxide semiconductor-based catalysts: effects of reaction temperature and metal oxide additives

The photo-oxidation of ethene and propene using zinc oxide and titanium oxide-based catalysts has been investigated at various reaction temperatures. The activity of the zinc oxide catalyst (0.25 g) was greatly enhanced when the reaction temperature was raised to 450–500 K, to afford 21 µmol h–1 of ethanal, 16 µmol h–1 of propenal and 49 µmol h–1 of carbon oxides, together with small amounts of propanal and methanal at 493 K. Loading of Group 5 or 6 metal oxide species on zinc oxide suppressed the formation of carbon oxides and propenal, whereas a significant formation of propanal was observed in addition to ethanal. Molybdenum oxide-loaded catalysts showed high selectivities toward oxygen-containing chemicals. Since the MoO3/SiO2 catalyst showed a similar product distribution in the photo-oxidation of propene, surface active centres including molybdenum species on zinc oxide surface seem to be responsible for the reaction. The use of titanium oxide-based catalysts at ambient temperature generally resulted in low selectivities toward oxygen-containing chemicals.