Tin oxide surfaces. Part 4.—Infrared study of the adsorption of oxygen and carbon monoxide + oxygen mixtures on tin(IV) oxide, and the adsorption of carbon dioxide on ammonia-pretreated tin(IV) oxide

Abstract

The transmission infrared technique has been used to study the adsorption of oxygen and carbon monoxide + oxygen mixtures on tin(IV) oxide. Adsorption of oxygen results in the appearance of two weak bands at 1155 and 1020 cm^–1 which did not shift using ¹⁸O-enriched oxygen. No assignment of the species responsible for these bands was made, but the accompanying broad intense band below 900 cm^–1 is associated with surface Sn—O—Sn bridges. Surface carbonate and bicarbonate species are formed slowly when the oxide is exposed to carbon monoxide + oxygen mixtures, essentially independent of the gas mixture composition in the range 10–70 % CO. No bulk reduction of the oxide was observed, in contrast to the behaviour previously observed with carbon monoxide alone. Hydration of the oxide surface prior to treatment with adsorbent severely inhibits the adsorption of carbon dioxide and carbon monoxide + oxygen mixtures. Preadsorbed ammonia has a similar inhibiting effect with carbon dioxide, but leads to the formation of a low stability carbamate salt of the unsubstituted carbamic acid, H₂NCO₂H.