INFLUENCE OF CARRIER DOPING ON THE INTERACTION OF BENZENE AND TOLUENEWITH SUPPORTED RHODIUM

The interaction of benzene and toluene with rhodium crystallites dispe rsed on TiO2 carriers doped with W6+ cations of variable concentration is investigated employing steady-state hydrogenation, competitive hyd rogenation, temperature-programmed desorption (TPD) and temperature-pr ogrammed surface reaction (TPSR). Turnover frequencies of both hydroge nation reactions are enhanced when Rh is dispersed on W6+-doped TiO2, while the ratio of the adsorption coefficients of toluene to benzene i s reduced. The latter result implies that the toluene-Rh interaction h as been weakened to a larger extent than the benzene-lih interaction. TPD and TPSR experiments also reveal weakened adsorption bands of benz ene and toluene with Rh supported on doped TiO,. These observations ar e discussed with respect to short-range and long-range electronic inte ractions at the metal-support interface, evoking the theory of metal-s emiconductor contacts. (C) 1995 Academic Press, Inc.