THE INTERACTION OF BENZENE AND TOLUENE WITH RH DISPERSED ON SIO2, AL2O3, AND TIO2 CARRIERS

The interaction of benzene and toluene with Rh dispersed on SiO2, Al2O3, and TiO2 carriers is investigated employing temperature-programmed desorption, temperature-programmed reaction and steady-state hydrogenation techniques. It is found that the aromatic molecules are weakly adsorbed on the carriers and are readily hydrogenated by spill-over hydrogen at room temperature. The surface coverage of benzene and toluene on Rh is found to be 0.39-0.42 and 0.34-0.38, respectively, following room temperature adsorption of 0.1 bar benzene or 0.03 bar toluene. Aromatic molecules adsorbed on Rh do not desorb molecularly, but dissociate at high temperatures producing hydrogen. Dehydrogenation reactivity is found to follow the order: Rh/TiO2 > Rh/Al2O3 > Rh/SiO2. Under hydrogen flow, only a small fraction of the adsorbed aromatic molecules is hydrogenated, and at sufficiently high temperatures the remainder is converted to CH4. Results of benzene hydrogenation under steady-state conditions are questioned in view of carrier participation in the reaction scheme. © 1993 Academic Press, Inc.