Surface characterization and catalytic activity of titania- and zirconia-supported tungsten catalysts

WO3/TiO2 and WO3/ZrO 2 catalysts were characterized using a variety of surface and bulk techniques. Attention has been focussed on the determination of the nature, abundance and dispersion of W on TiO2 and ZrO2 supports.; The surface coverage of a series of WO3/TiO2 catalysts prepared by incipient wetness impregnation was determined by CO2 chemisorption and compared with those previously obtained using ISS. The main objective was to evaluate the use of CO2 chemisorption method for the determination of surface coverage of TiO2-supported catalysts. In contrast to alumina-supported catalysts, it was observed that CO2 chemisorption method can be used successfully to monitor the surface coverage of WO3/TiO2 catalysts.; Coverage measurements were also carried out on a series of WO3/ZrO 2 catalysts using ISS and low temperature CO adsorption. It was observed that comparable values were obtained using ISS and CO adsorption. Thus, as reported previously for alumina-supported catalysts, the joint use of ISS and CO adsorption were shown to be effective for surface coverage measurements.; The oxidic WO3/ZrO2 catalysts were also characterized using XRD, Raman, XPS and IR. XRD and Raman spectroscopy showed that the ZrO 2 support was present predominantly in the monoclinic form. XPS and Raman measurements showed the formation of increasing amounts of W interaction species for catalysts with W loadings ≤8.8 wt% WO3. In addition to the W interaction species, bulk WO3 was also observed for catalysts with W loadings ≤3.0 wt% WO3. Analysis of the hydroxyl region of ZrO2 by IR indicated that initial additions of W occurs on the high frequency hydroxyl group. Based on the results obtained using the various techniques, a structure for the WO3/ZrO2 catalysts has been proposed.; Isopropanol decomposition activity was studied on the series of WO 3/ZrO2 catalysts. The main objective was to investigate the correlation between the nature, abundance and dispersion of the W species on the ZrO2 support and the isopropanol decomposition activity. Comparison of the structure and activity suggested that the W species formed by the interaction with the isolated hydroxyl groups were not active for the reaction. The polymeric W species that do not interact with the isolated hydroxyl group of ZrO. form the active sites. This has been tentatively attributed to the development on Bronsted acidity on these catalysts under reaction conditions.; The distribution of W oxidation states on a high loading (28.4 wt%) WO 3/TiO2 catalyst was determined using XPS in conjunction with deconvolution, curve fitting and factor analysis. The results were compared to those obtained on a 5 wt% catalyst reported earlier to determine the effect of bulk WO3 on the reduction process. It was observed that the presence of bulk WO3 on the 28.4 wt% catalyst did not significantly affect the overall reduction process.