Diffuse reflection IR spectra study of the surface of yttrium, erbium and holmium oxides. II. Aprotic sites

The IR spectra of adsorbed CO and H2 molecules were used to study the aprotic sites formed upon dehydroxylation of Y2O3, Er2O3, and Ho2O3 surfaces. Two types of acid-base pairs (M-O) are found in the oxides aged at 873-1073 K, which are capable of adsorbing CO in the molecular form at low temperatures and displaying either electron-withdrawing or electron-donor properties. The electron donor M-O pairs strongly polarize H2 molecules adsorbed at 77 K and display high reactivity of ≥ 195 K in the formation of various surface compounds (ketenes, conjugated five- and six-membered (CO)n2- species, and carbonates). Furthermore, the oxide surfaces feature two types of aprotic sites, which are highly basic, incompletely coordinated O2- anions. Two types of dioxoketenes differing in the frequencies of the asymmetrical C=C=O vibrations and reactivity toward CO molecules are formed from CO on these sites