XPS intensities and binding energy shifts as metal dispersion parameters in Ni/SiO ₂ catalysts

A set of Ni/SiO 2 catalysts with metal loadings between 1 and 8% by weight has been prepared by several methods. Metal dispersions have been determined by H 2 chemisorption and x‐ray line broadening analysis, giving metal particle sizes from ∼30 to 250 Å. XPS analysis of the samples has been recorded after reduction in situ and the data correlated with the metal loading and metal dispersion. When comparing the Ni 2p intensities, a good relationship has been obtained with metal surface concentration, showing the existence of two well‐defined set of catalysts with particles of quite different sizes. However, a single linear relationship is obtained for all the samples when the Ni 2p binding energies are plotted against the metal dispersion calculated from H 2 chemisorption. The origin of the binding energy shift and its relation with metal dispersion is discussed.