APPLICATION OF XPS TO THE DETERMINATION OF THE SIZE OF SUPPORTED PARTICLES IN A CATALYST-MODEL DEVELOPMENT AND ITS APPLICATION TO DESCRIBE THE SINTERING BEHAVIOR OF A SILICA-SUPPORTED PT FILM

A general expression relating the observed XPS intensity ratio of the dispersed phase to the carrier of a catalyst with the size of the dispersed particles has been derived. The shape of the supported particles dictates the type of functional relationship which exists between the observed XPS intensity ratio and the size of the supported particles. This functional relationship has been derived for spherical, hemispherical, and cubic particles. The chemical nature of the catalyst is expressed as a parameter, λc(E), describing the mean free path for inelastic scattering of the dispersed-phase photoelectrons in the supported particles. A special case can be generated from this general expression to account for a linear relationship of the loading of the dispersed phase with the observed XPS dispersed phase/carrier intensity ratio provided that there is no maldistribution of the supported particles on the surface of the carrier. The derived expression is utilized successfully to describe the sintering behavior of a monoatomic Pt film on a silica substrate under hydrogen. © 1979.