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Ion scattering analysis of rhodium adlayers on alumina films

Rhodium shows catalytic activities for a variety of chemical reactions. Its flexibility, as regards reactivity in carbon monoxide hydrogenation, makes it very interesting for the examination of catalytic mechanisms. Moreover, rhodium and other group VIII metals have been found to show strong interactions between the metal and typically reducible oxidic supports such as titanium dioxide (SMSI, strong metal support interactions). Similar effects have also been reported with non-reducible supports such as alumina.

To study systems with surface sensitive methods using charged particles, it is convenient or even necessary that the samples show sufficient electrical conductivity. In this work, thin oxide films prepared by anodic oxidation of aluminium exhibited no disturbing charging effects. Model systems for rhodium/alumina catalysts with metal loadings of one monolayer were prepared and characterised by Ion Scattering Spectroscopy (ISS) and Rutherford Backscattering Spectroscopy (RBS).

It was shown that alumina layers up to some hundred angstroms thick have a sufficiently high electrical conductivity to be examined with ion beam methods. The surface of the anodically prepared oxide films is much larger than the geometric area of the specimen. Their thickness can be increased by calcination of the samples. The distribution of oxygen in the calcined alumina layer is inhomogeneous, the stoichiometry changing continuously from alumina to metallic aluminium with increasing depth. The metal was uniformly distributed over the samples, and no indication of clustering or island formation was found. Due to the large oxide surface, the rhodium does not cover the support completely.

Reported by

Max-Planck-Institut fuer Plasmaphysik
Boltzmannstrasse 2
85748 Garching bei Muenchen
Germany
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