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.