Surface reactivity of SnO2 obtained by sol-gel type condensation: Interaction with inert, combustible gases, vapour-phase H2O and air, as revealed by electron paramagnetic resonance spectroscopy

Electron paramagnetic resonance (EPR) studies have been carried out on lattice oxygen vacancies produced by the interaction of carbon monoxide with SnO2 obtained by sol-gel type condensation. Under a 0.5% CO-argon reducing atmosphere the vacancies can transfer electrons to Sn4+ producing Sn2+ centres. In air the lattice defects interact with molecular oxygen in a manner which depends on whether the gas reducing treatment was performed under dry or moist conditions. Defects that undergo oxygen interaction at the SnO2 surface, reduce O-2 to O-2(-) or O2-, depending on the temperature of the reaction with oxygen.