The slurry-phase hydrogenation of aromatic compounds such as benzene, naphthalene and biphenyl is used to investigate the influence of altervalent carrier doping on the specific hydrogenation activity of Pt, Rh, Ru and Pd catalysts. The metals are dispersed on TiO2 carriers doped with cations of valence higher than that of the parent cation, such as W6+ and Ta5+. Doping is achieved by high temperature diffusion of the doping cation into the crystal lattice of the carrier. It is shown that the hydrogen adsorption capacity of Rh, Ru and Pd is enhanced upon doping of the carrier and the degree of enhancement is a function of dopant concentration in the carrier. The same metals also exhibit enhanced activity for benzene, naphthalene and biphenyl hydrogenation and improved sulfur tolerance when thiophene is used as the sulfur source. Platinum, however, exhibits reduced hydrogen uptake capacity and hydrogenation activity when it is dispersed on higher-valence doped TiO2 carriers. These observations are interpreted in terms of an electronic interaction developing at the metal-support interface, as a result of the doping process, which causes a lowering of the work function of surface metal atoms.
- aromatic compounds
- noble metal catalysts