Abstract
Sulphur adsorption on Cu covered Rh(111) surfaces, prepared as models of “bimetallic cluster” catalysts, was studied and the effects of preadsorbed sulphur on the chemisorption of CO and C 2H 2 on Rh(111)-Cu surfaces examined. In the initial stages of the interaction of sulphur with the metal, strongly bound adsorbate overlayers are formed, while epitaxial sulphide growth takes place at higher sulphur exposures. Sulphur adsorbs indiscriminately on the two components in the bimetallic interface during overlayer formation; preferential formation of Rh 2S 3 is observed, however, at higher sulphur loadings. Sulphur overlayers block the chemisorption of CO and C 2H 2 although blocking is not complete at sulphur concentrations below 8.0 × 10 18 atoms m −2. The extent of adsorption of C 2H 2 falls much more rapidly with increased sulphur coverage than does CO chemisorption, showing that C 2H 2 adsorption requires the larger ensemble size of Rh atoms. Sulphur produces a weakening of the CO adsorption bond by 29 kJ mol −1 but has no effect on the energetics of ethylidyne decomposition.
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