Role of Sulfur in Catalytic Hydrogenation Reactions

Abstract

This chapter discusses the role of sulfur in catalytic hydrogenation reactions. One of the most severe causes of metallic catalyst poisoning is the adsorption of species containing sulfur. Sulfur-containing compounds are present in natural sources of hydrocarbons, and are found in industrial feedstocks. The poisoning of metallic catalysts by sulfur has been extensively studied, essentially on nickel, palladium, and platinum, for numerous reactions and consequently under very different experimental conditions, particularly for temperatures ranging from 300 to 1300 K. Such desorptions, depending on the metal-sulfur binding energy and the thermodynamic properties of the surface-adlayer interface, play an important role in controlling the sulfur coverage. The distribution of adsorbed sulfur on the metallic surface and the resulting effect on activity and selectivity of the metal depends on this coverage. At low coverage, for which interactions between adjacent adatoms are negligible, sulfur atoms adsorbed on a heterogeneous surface are located on sites that have the highest binding energies. At higher coverages, sulfur atoms could be gathered into islands. Catalytic reactions performed at low temperatures (below 400 K) show that adsorption of sulfur-containing compounds is then irreversible, the equilibrium being wholly displaced toward the left.