Model experiments on the poisoning of Pt catalysts by sulfur

Abstract

Surface reactions have been studied in high vacuum on the (100) surface of platinum that was clean or covered with various amounts of sulfur. This system was chosen for its simplicity in order to observe the mechanisms by which sulfur poisons catalytic activity. Three different poisoning mechanisms were identified: (i) When the surface is covered with one S atom per two surface Pt atoms, it is chemically inert, (ii) At lower coverages, the strong chemical bond to sulfur modifies the chemical properties of the platinum surface and weakens its interaction with adsorbates. (iii) When the sulfur coverage is one S per four Pt, a regular sulfur overlayer is established; molecules can adsorb on the surface but are prevented by the sulfur structure from participating in Langmuir-Hinshelwood reactions. The reactions on which these observations were made are the dissociation of H 2S, the adsorption and desorption of CO, the reduction of NO by CO, the dissociation and desorption of NO, and the adsorption and dehydrogenation of benzene and acetylene.