Infrared study of surface chemistry and electronic effects of different atmospheres on SnO2

Abstract

An i.r. study is made of the room-temperature adsorption of pure CO, H₂ and successive O₂ interaction on SnO₂ powder at different degrees of hydroxylation. Both sharp bands, due to different adsorbed carbonate-like species produced by surface reactions, and a very broad absorption, due to electron transition from the second level of oxygen vacancies to the conduction band, are measured in the case of the CO interaction. A wider variety (bicarbonates, unidentate and bidentate carbonates) and larger amounts of such intermediates are measured on highly-hydroxylated surfaces (h.h.s.) than on less-hydroxylated (l.h.) ones. At the same time, the intensity of the electronic transition is higher for h.h.s. than l.h. ones. A very broad absorption due to the same electronic transition can be detected for H₂ admission; however, no increase in the band intensities due to the vibrations of surface hydroxyls can be measured.