HYDROGEN ADSORPTION ON RHODIUM PARTICLES SUPPORTED ON STRONTIUM-TITANATE AS FOLLOWED BY H-1-NMR AND MICROCALORIMETRY

Hydrogen adsorption on supported rhodium particles has been studied by H-1 NMR, volumetry, and microcalorimetry techniques, The amounts of h ydrogen adsorbed on the metal and support have been evaluated. There i s a good correlation between the shift of the NMR Line assigned to hyd rogen adsorbed on the metal and the mean integral heat involved in thi s adsorption. This permits an estimation of differential shifts corres ponding to each dose. From analysis of differential NMR shift and diff erential adsorption heat, it is deduced that the hydrogen-metal intera ction becomes weaker and less energetic with adsorption. This effect i s discussed on the basis of the heterogeneity of the adsorption sites and a modification of the electronic properties at the metal surface.