Tin oxide surfaces. Part 1.—Surface hydroxyl groups and the chemisorption of carbon dioxide and carbon monoxide on tin(IV) oxide

The transmission infra-red technique has been used to investigate the surface of tin(IV) oxide as a function of evacuation temperature in the range 293–773 K. Molecular water is largely removed by evacuation at 320 K and is fully removed at 473 K. Hydrogen-bonded hydroxyl groups are present after evacuation at 773 K, and isolated hydroxyl groups exhibit a stretching frequency at 3640 cm–1. Room temperature carbon dioxide adsorption has been studied as a function of thermal pretreatment in the range 320–618 K and the spectra obtained indicate a surface carbonate and a surface bicarbonate. The adsorption of carbon monoxide has been investigated in a similar manner. A carbonate species is proposed from the infra-red data, and the partial reduction of the tin(IV) oxide to a tin(II) species has been confirmed by tin-119 m Mössbauer spectroscopy. No evidence was obtained for the physical adsorption of either carbon dioxide or carbon monoxide.