Influence of carrier doping on the interaction of benzene and toluene with supported rhodium

The interaction of benzene and toluene with rhodium crystallites dispersed on TiO₂ carriers doped with W⁶⁺ cations of variable concentration is investigated employing steady-state hydrogenation, competitive hydrogenation, temperature-programmed desorption (TPD) and temperature-programmed surface reaction (TPSR). Turnover frequencies of both hydrogenation reactions are enhanced when Rh is dispersed on W⁶⁺-doped TiO₂, while the ratio of the adsorption coefficients of toluene to benzene is reduced. The latter result implies that the toluene-Rh interaction has been weakened to a larger extent than the benzene-Rh interaction. TPD and TPSR experiments also reveal weakened adsorption bands of benzene and toluene with Rh supported on doped TiO₂. These observations are discussed with respect to short-range and long-range electronic interactions at the metal-support interface, evoking the theory of metal-semiconductor contacts.