FTIR studies on the selective oxidation and combustion of light hydrocarbons at metal oxide surfaces Part 3.—Comparison of the oxidation of C3 organic compounds over Co3O4, MgCr2O4 and CuO
Oxidation of the C 3 organic compounds propane, propene, acrolein, propan-2-ol and acetone has been investigated over three transition-metal oxide catalysts, Co 3 O 4 , MgCr 2 O 4 and CuO, in a flow reactor and using FTIR spectroscopy to study the adsorbed species. Co 3 O 4 and MgCr 2 O 4 are very active in propane and propene catalytic combustion. FTIR studies suggest that adsorbed isopropoxide species and adsorbed acetone and acetates are intermediates in propane oxidation while adsorbed acrolein and acrylates are intermediates in propene oxidation. Flow reactor studies support these hypotheses. It is suggested that the reaction rates in propane and propene total oxidation can be influenced, at low temperature, by the rate of oxidation of adsorbed acetate and acrylate intermediates, respectively. Co 3 O 4 and MgCr 2 O 4 are also active and quite selective catalysts for the oxy-dehydrogenation of propan-2-ol to acetone at low conversion, suggesting that the same oxygen species are involved in total and partial oxidation of organic compounds. CuO, as such, is not active in the adsorption and oxidation of C 3 hydrocarbons and oxygenates, at low temperature. At higher temperatures the reactants reduce the catalyst and catalytic activity starts. The oxidation state of the CuO x catalyst can be evaluated by IR studying the transmittance of the radiation upon different treatments.