SURFACE REACTIVITY OF SNO2 OBTAINED BY SOL-GEL TYPE CONDENSATION - INTERACTION WITH INERT, COMBUSTIBLE GASES, VAPOR-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 monoxi de with SnO2 obtained by sol-gel type condensation. Under a 0.5% CO-ar gon reducing atmosphere the vacancies can transfer electrons to Sn4+ p roducing Sn2+ centres. In air the lattice defects interact with molecu lar oxygen in a manner which depends on whether the gas reducing treat ment 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.