Carbon monoxide and carbon dioxide adsorption on cerium oxide studied by Fourier-transform infrared spectroscopy. Part 1.—Formation of carbonate species on dehydroxylated CeO2, at room temperature

Abstract

The adsorption of CO and CO2 on cerium oxide has been studied by Fourier-transform infrared spectroscopy (F.t.i.r.). For CO adsorption at room temperature, in addition to linearly adsorbed CO (2177 and 2156 cm–1), two kinds of carbonate (unidentate: 854, 1062, 1348 and 1454 cm–1 and bidentate: 854, 1028, 1286 and 1562 cm–1) and inorganic carboxylate (1310 and 15⊙0 cm–1) species were identified spectroscopically. As for CO2 adsorption, apart from weak bands at 1728, 1396, 1219, and 1132 cm–1 attributed to bridged carbonate species, bands due to unidentate carbonate, bidentate carbonate and inorganic carboxylate species, similar to those aising from CO adsorption, were observed. Except for the linearly adsorbed-CO, all species arising from CO and CO2 are stable at room temperature in vacuo. The desorption of these species at elevated temperatures shows that the order of thermal stability is bridged carbonate <bidentate carbonate < inorganic carboxylate < unidentate carbonate species, and the residual of unidentate carbonate species can remain on the surface up to 773 K under evacuation. Forming carbonte and inorganic carboxylate species proved that the CeO2 surface could be partially reduced by CO even at room temperature. No bands in the region 2300–800 cm–1 were detected below 373 K for CO adsorption on hydroxylated CeO2. This indicates that CO adsorption depends on the degree off dehydroxylation of the surface. The mechanism of CO adsorption is also discussed.