Transfer of concepts from homogeneous to heterogeneous catalysis, use of Hammett relationships to assess reaction mechanisms and nature of active sites in reactions catalyzed by sulfides, metals, clays and zeolites

The application of Hammett or Hammett-type relationships to a series of various reactions catalyzed by clays, zeolites, sulfides and metals is reviewed in this paper. Such relationships are, of course, of great interest for a better knowledge of the reaction mechanisms over solid catalysts and on the nature of the active species, Among the different data obtained in the laboratory over those catalytic systems, it appears that Hammett slope rho values for the acid-catalyzed reactions involving Bronsted species in the rate-determining step (hydration, hydrolysis, isomerization, electrophilic aromatic substitution) are of the same order of magnitude for both homogeneous and heterogeneous reactions, whereas deviations are more frequently observed for reactions involving hydrogen.