Interactions of tin oxide surface with O2, H2O AND H2

Interactions of tin oxide surface with oxygen, water vapor, and hydrogen have been investigated. Temperature programmed desorption (TPD) chromatograms of oxygen showed the formation of four kinds of oxygen species on SnO2 which were desorbed around 80°C (α1), 150°C (α2), 560°C (β), and above 600°C (γ), respectively, on heating at 20°C/min. Based on electric conductivity and ESR measurements, these species were assigned as O2 (α1), O2− (α2). O− or O2− (β), and a part of lattice oxygen (γ), respectively. Two types of water adsorption were indicated by broad TPD peaks centered at 100°C (ga) and 400° C (β), for which molecular and dissociative (surface hydroxyls) adsorbates were assigned respectively. Of these, β caused an increase in electric conductivity of SnO2. The interactions of H2 with SnO2 surface were complicated by the reduction of SnO2 taking place at higher temperature. Exposure of evacuated SnO2 to h2 at room temperature gave a large TPD peak centered at 100°C (α). After cooling in H2 from 200°C to room temperature, however, large amounts of H2O desorption were observed, in addition to the H2 desorptions around 100°C (α) and 220°C (β). The type α was shown to be of depletive type. These phenomena are discussed briefly in relation to the actual case of gas detection.