Sulfide Catalysts for the Hydrogenation of Aromatic Hydrocarbons: III. Mechanism of Benzene Hydrogenation
Kinetics and Catalysis
, E-ISSN: 1608-3210
Boreskov Institute of Catalysis SB RAS
A simple and efficient procedure was proposed for the determination of the amount of hydrogen sulfide removed from the surface of sulfide catalysts during their activation by the hydrogen-benzene mixture. It is shown that, to obtain the active form of a Ni-W catalyst for benzene hydrogenation, approximately one sulfur atom per one nickel atom should be removed from the catalyst surface. In the case of a Ni-Mo catalyst, this value is 0.6-1.0. A possible structure of the active sites of hydrogenolysis and hydrogenation catalysts and their interconversions during catalysis are discussed. In both cases, thiophene and benzene molecules are adsorbed on nickel atoms in the active component, which is a bimetallic sulfide. It is assumed that the chemisorption properties of nickel in a bimetallic sulfide are determined by its unusual d(6)-electron configuration, which is "maintained" by adsorbed molecules. A hypothesis was advanced that the electronic structure of nickel is formed by the oxidative addition of hydrogen during the sulfidization of the catalysts at the stage of their activation. A concerted mechanism of benzene hydrogenation on bimetallic sulfide with any chemical composition was suggested.