The role of adsorbed sulfur in the H2D2 equilibration reaction on Pt single crystals |
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Authors: | CM Pradier Y Berthier J Oudar |
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Institution: | Laboratoire de Physico-Chimie des Surfaces, associé au CNRS, ERA 313, Université Pierre et Marie Curie, ENSCP, 11 Rue Pierre et Marie Curie, F-75005 Paris, France |
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Abstract: | The H2D2 equilibration on Pt single crystals was investigated under intermediate pressure (100–400 Torr) and temperature (50–250°C), as a function of sulfur coverage. On Pt(110) and Pt(111), adsorbed sulfur modifies the kinetic parameters, activation energy and pre-exponential factor; the latter depends on the temperature on Pt(110) only. The clean Pt(110) face was found to be 5 times more active than the clean Pt(111). On both faces, adsorption of sulfur induces electronic effects on the neighbouring reactional sites. The difference in the behaviour of the two faces and a clear influence of the arrangement of the adsorbed sulfur atoms, deduced from LEED diagrams, tend to prove the structure dependency of the H2D2 reaction. A consistent reaction mechanism could be proposed, involving the dissociative adsorption and surface recombination of hydrogen and deuterium, and the reaction between adsorbed molecules for high sulfur coverages. The value of the sulfur coverage which makes the platinum inactive towards H2D2 is lower for the (111) than for the (110) orientation; this is in correlation with the roughness of the surface; the denser at atomic scale a surface is, the further is the extent of the lateral interactions due to adsorbed sulfur. |
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