Ion scattering and electron spectroscopic study of the surface coverage of V/Al2O3 catalysts

Ion scattering spectroscopy (ISS) and x-ray photoelectron spectroscopy (XPS, ESCA) were used to study the dispersion of the vanadium phase and the coverage of Al2O3 by vanadium. A series of V/Al2O3 catalysts was prepared by equilibrium adsorption with vanadium loadings varying from 1.9 to 6.7 wt.% V. By monitoring the ISS Al/O intensity ratio the surface coverage of the catalysts was determined. The surface coverage increases from 15 to 33% with increasing the loading from 1.9 to 3.5 wt.% V. The results are consistent with a model of a uniform monolayer vanadium phase. For higher vanadium loadings the surface coverage appears to level off, suggesting the formation of a multilayer vanadium phase.