COMPETITIVE HYDROGENATION OF BENZENE AND TOLUENE - THEORETICAL-STUDY OF THEIR ADSORPTION ON RUTHENIUM, RHODIUM, AND PALLADIUM

Benzene and toluene adsorption on hexagonally close packed Pd, Rh, and Ru surfaces has been studied by semiempirical method. Simple MO arguments, supported by extended Mickel calculations, are used to show that toluene is more strongly adsorbed than benzene (the energy gap between the frontier orbitals is smaller and the bending of the methyl group removes the steric repulsion). The differences in the ease of adsorption on the different metals induce differences in the competitive hydrogenation reactions. These differences are increased by the presence of acceptor coadsorbates which induce a shift of the surface work function to large values. © 1990.