FTIR study of low-temperature adsorption and co-adsorption of 12CO and 13CO on a TiO 2–SiO 2 mixed oxide

Abstract

Adsorption of 12CO on a TiO 2−SiO 2 sample prepared via the homogeneous precipitation method (Ti : Si molar ratio 1 : 1) is negligible at ambient temperature. At 85 K, however, different sites are monitored by CO: two kinds of Ti 4+ cations ( ν CO at 2185–2199 and 2173–2177 cm −1, respectively) and CO attached to surface silanol groups (2156 cm −1). Although the higher frequency carbonyls are more stable, all species disappear after evacuation at 85 K. The Ti 4+−CO band positions are coverage dependent: the first band is shifted from 2199 cm −1 at low coverage to 2185 cm −1 at high coverage, while the second band shifts from 2177 cm −1 at low coverage to 2173 cm −1 at high coverage. Co-adsorption of 12CO– 13CO isotopic mixtures reveals that these shifts are entirely static in character. Some conclusions about the acidity and distribution of the Ti 4+ cations on the sample surface are drawn.