The chemistry and catalysis of the water/toluene reaction 1. The specific activities and selectivities of the Group VIII metals supported on Al2O3

The reaction of steam with heavy hydrocarbons to produce liquids and light gases is an attractive alternative to hydrocracking in that expensive hydrogen is replaced by water. In this and the following paper, investigations of the chemistry and catalysis of the selective steam dealky-lation reaction over the Group VIII metals are reported. The first paper will discuss the specific activities and selectivities of the Group VIII metals supported on alumina for the model reaction of water and toluene to produce benzene, carbon oxides, and hydrogen. The relative specific activities (rates per surface metal atom) for benzene formation of the Group VIII metals/Al2O3 are: Rh, 100; Ru, 52; Pd, 34; Pt, 21; Ir, 14; Ni, 9; Os, 3. The selectivities (molecules of benzene formed per molecule of toluene reacted) of the supported metals are: Pd, Pt, 0.95–1.00; Rh, Ir, 0.85–0.90; Ru, Os, 0.60–0.70; Ni, 0.40. Studies of the dependence of rate on the partial pressures of water and toluene over the Group VIII metals are reported for the first time. For toluene the dependence of rate on partial pressure varies from −0.13 to +0.26, whereas for water the variation is from 0.25 to 0.67. Where possible, these results are compared to those of other workers. For example, the specific activities of Rh, Pd, and Pt reported here show good agreement with values reported previously for these metals. In all cases, rhodium is found to be the most active metal for the water/toluene reaction.