Surface coverage of WO3/ZrO2 catalysts measured by ion scattering spectroscopy and low temperature CO adsorption

A series of WO3/ZrO2 catalysts with tungsten (W) loadings varying from 0.5 to 11.4 wt.% WO3 was prepared by incipient wetness impregnation. The surface coverage of these catalysts was monitored by ion scattering spectroscopy (ISS) and low-temperature CO adsorption. Comparable values for the surface coverage were obtained from ISS and CO adsorption. The surface coverage as determined by these two independent techniques increased from zero to 51±3% as the W loading increased from zero to 4.5 wt% WO3, and leveled off at ∽54±3% with further increases in W loadings. For catalysts with W loadings <3.0 wt.% WO3, the surface coverage values were in reasonable agreement with those predicted assuming a monolayer dispersion. For higher W loadings, the results were consistent with multilayer or WO3 formation. This study gives further support for the proposed methodology for monitoring the surface coverage of supported catalyst systems.