On the stepwise change of activation energies in the hydrodechlorination of chlorobenzene over supported nickel

Kinetics of chlorobenzene hydrodechlorination have been measured over Ni on SiO₂, Al₂O₃, MgO, activated carbon and graphite. A stepwise variation of E_a is analysed using the selective energy transfer model where E_a is identified as the vibrational energy associated with an excitation of the chlorobenzene out-of-plane C-H bending mode. Variation of E_a with vibrational quantum number yields a vibrational frequency of 749 cm^-1 and a value (-1.1 cm^-1) for the anharmonicity term, which is characteristic of bending vibrational modes. Our analysis suggests that the reacting species are weakly adsorbed on the catalyst: heat of adsorption = -0.31 kJ mol^-1. © 2007 Elsevier B.V. All rights reserved.