ELECTRICAL-CONDUCTIVITY CHARACTERIZATION OF EUROCAT TITANIA-SUPPORTEDVANADIA CATALYSTS

Two Eurocat V2O5/TiO2 Catalysts (EL10V1 and EL10V8), were characterize d by electrical conductivity measurement at 300-degrees-C. It was demo nstrated that vanadium is partially dissolved as V5+ ions into the lat tice of TiO2 during the preparative calcination. The concentration of dissolved V5+ ions increases with the amount of deposited vanadia and concordant results indicate that 2.5 times more V5+ ions are dissolved in the sample supporting 8 wt.-%/V2O5 than in that supporting only 1 wt.-% V2O5. The major part Of V2O5 is present as deposited particles. There is an indirect evidence (i) for the absence of a regular and con tinuous V2O5 surface layer model and (ii) for an increase in the mean particle size as the percentage of deposited V2O5 increases. At a high er temperature (450-degrees-C), equal to the final calcination tempera ture during catalyst preparation, anionic vacancies were detected at t he surface of TiO2 and are in equilibrium with gaseous oxygen. Their c oncentration in TiO2 increases with the content of deposited V2O5. Con sequently, TiO2 appears as a non-inert support and should intervene in the catalytic performance of the solid. Etching in boiling isobutanol selectively removes V2O5-supported particles but does not destroy the solid solution of V5+ in TiO2. A schematic representation is proposed for the two catalysts tested: this consists of a solid solution (V5in TiO2) supporting V2O5 particles. The solubility of V5+ and the mean particle size (with the assumption of homodispersed particles) both i ncrease with the percentage of deposited vanadia (2-3 nm and 15-20 nm for V2O5 particles in EL10V1 and EL10V8 samples, respectively).