Oxidation state of Ce and ethanol–oxygen reaction of mesoporous titania-supported cerium oxide

Cerium-incorporated mesoporous titania, Ce-meso TiO2, was prepared by the co-condensation method using Ce(NH4)2(NO3)6 and Ti(OiC3H7)4 as precursors and n-dodecylamine as a structural directing agent. The catalysts obtained had high surface area and narrow pore size distribution similar to mesoporous titania. The population of Ce(III) in these catalysts was investigated by XANES spectroscopy. Although the precursor was tetravalent, the concentration of Ce(III) was nearly 100% and 80% in Ce-meso TiO2 catalysts prepared with the precursor mixing ratios of Ti/Ce = 20 and 50, respectively. In Ce-meso TiO2 prepared with Ti/Ce = 100, the concentration increased from 39% to 69% after the calcination from 473 K to 673 K. In the catalyst prepared without n-dodecylamine, the concentration was only 30%, which is almost the same as the value obtained for P-25 supported Ce catalyst. These results imply that the lower valence becomes stable by the presence of mesoporous titania framework. In the ethanol–oxygen reaction, ethylene and carbon dioxide were formed on the Ce/P-25 catalyst. The activity and selectivity depended little on the calcination temperature of the catalyst, which concurs with the constant concentration of Ce(III). On the other hand, the main products on the Ce-meso TiO2 catalyst were acetaldehyde and acetic acid. The selectivity for acetic acid increased with the calcination temperature of the catalyst. The concentration of trivalent Ce was correlated with the formation of acetic acid. Additionally, the local structure of Ti in the Ce-meso TiO2 catalyst was investigated by Raman spectroscopy. The structure of the support framework had little influence on the ethanol–oxygen reaction.