CHEMISTRY AND CATALYSIS OF THE TOLUENE HYDRODEALKYLATION REACTION .1. SPECIFIC ACTIVITIES AND SELECTIVITIES OF GROUP VIIB AND GROUP VIII METALS SUPPORTED ON ALUMINA

The catalytic hydrodealkylation of alkylaromatics is a reaction of continued industrial interest. In this and the following paper, investigations of the chemistry and catalysis of the hydrodealkylation reaction over supported metals are reported. The first paper will discuss the specific activities and selectivities of alumina-supported Group VIIB and Group VIII metals for the model reaction of toluene and hydrogen to produce benzene and methane. The relative specific activities (rates per surface metal atom) of the metals for benzene formation at 380 °C are: Ni, 1000; Rh, 329; Ir, 177; Os, 69; Ru, 47; Pt, 9; Pd, 2; Re, 1. The selectivities (molecules benzene formed per toluene molecule reacted) of these metals are: Pd, 1.0; Rh, 0.98; Pt, 0.96; Ir, 0.95; Ni, 0.94; Os, 0.93; Re, 0.85; Ru, 0.82. The dependence of rate on the partial pressures of hydrogen and toluene over these metals are reported for the first time. For hydrogen the dependence of rate on partial pressure varies from -0.39 for Pd to 1.65 for Re. The dependence of rate on toluene partial pressure varies from -0.17 for Re to 0.47 for Pt and Pd. The magnitudes and periodic trends of these kinetic parameters are found to be substantially different from the periodic trends of these metals previously observed for other CC bond breaking reactions such as ethane hydrogenolysis. Where possible the results of this present study are compared to those of other workers. For example, the specific activities of Rh and Pd reported here are in good agreement with results previously reported, but differ substantially for the specific activities of Ru and Pt. In agreement with this study, the previous studies point to rhodium as the most active noble metal for the toluene hydrodealkylation reaction. © 1979.