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).