Catalyst metal-support interactions: Rutherford backscattering spectrometry applied to discontinuous films

Abstract

Catalyst surfaces are generally prepared with finely divided metal particles dispersed over a rough porous ceramic "support" substrate. Application of standard analysis techniques to such inhomogenous surfaces has been regarded as virtually impossible. However, the powerful effects of supposedly passive support materials on the performance of catalyst surfaces have led to a great need to understand the "Strong Metal-Support Interactions" (SMSI) in these materials. We have demonstrated that Rutherford backscattering spectrometry (RBS) can be applied to even such difficult questions. In the Present work, the metal/ceramic systems were modeled with thin films of Pt or Rh deposited on single-crystal substrates of Al2O3 or TiO2 and subjected to extended heat treatment in various atmospheres. The metals do not in general "wet" the support surface, and hence they break up into islands. Nevertheless, careful RBS analysis of composition profiles for these discontinuous layers, together with electron microscopy, has enabled us to unravel a complex chain of diffusion/reaction processes which seems to account for the SMSI effects in these systems. © 1983.