Concerted mechanisms in heterogeneous catalysis by sulfides

This paper summarizes some new evidence for the possibility of concerted mechanisms in the heterogeneous catalysis by sulfides. Several aspects are discussed: main regularities of thiophene and THT hydrogenolysis mediated by the well-characterized sulfide catalysts of different composition; electronic structure of the metals entering into the composition of the active component of both bulk and supported sulfide catalysts; mechanism of the active centers formation cased by the oxidative addition of dihydrogen to the active Ni (Co) metals and occlusion of hydrogen atoms into the MoS2 matrix; mechanism of the homolytic hydrogen adsorption on the sulfide hydrotreating catalysts; synchronous interaction of the reactive molecules in the coordination sphere of the bimetallic active centers - proton and electron transfer; use of the energy released:during exothermic reaction steps in the catalytic cycle. Catalytic transformations over the sulfide HDS catalysts are considered to belong to the acid-base catalysis. The profound identity of the mechanisms of heterogeneous, homogeneous and enzyme catalysis is discussed. (C) 2000 Elsevier Science B.V. All rights reserved.