MONITORING THE SURFACE COVERAGE OF W/TIO2 CATALYSTS BY ION-SCATTERING SPECTROSCOPY

A series of W/TiO2 catalysts was prepared by incipient wetness impregnation with W loadings varying from 1.64 to 28.4 wt.% WO3. The coverage of the TiO2 surface by W species was monitored by ion scattering spectroscopy (ISS). The results indicated that the W coverage increased from 21.6% for the 1.64 wt.% WO3/TiO2 catalyst to similar to 85% for catalysts with W loadings greater than or equal to 10.3 wt.% WO3. These values agreed with those predicted from monolayer-like dispersion. The relatively constant coverage for W loadings > 10.3 wt,% WO3 was taken as an indication of multilayer or WO3 formation, These results were consistent with Raman and x-ray photoelectron spectroscopy (XPS) data previously obtained in our laboratory.