SURFACE DYNAMICS IN TIN DIOXIDE-CONTAINING CATALYSTS .3. CATALYSIS AND THE SURFACE CONDUCTIVITY OF ANTIMONY-DOPED TIN DIOXIDE

The variation of surface conductivity of SnO2, Sb2O3 and of antimony-d oped tin dioxide in air, argon, propylene-air, and propylene-argon mix tures has been followed in situ between room temperature and 400 degre es C. The apparent p-type behavior of some of the antimony-doped sampl es was explained by fluctuations in the concentration of the surface d efects caused by variation of the ratio of coexisting Sb3+ and Sb5+ io ns. Thermogravimetric data indicate increased lattice mobility on anti mony doping. It is suggested that the high electronic conductivity res ulting from the presence of antimony in the SnO2 matrix is related wit h the increased structural disorder; consequently, the increased rate of the reoxidation step prevents surface contamination with strongly a dsorbed hydrocarbon species.