Kinetics of toluene hydrogenation on a supported nickel catalyst

Abstract

The gas-phase hydrogenation of toluene to methylcyclohexane was studied on a noncommercial supported nickel catalyst. The reaction kinetics were investigated in a differential reactor operating at atmospheric pressure and temperatures between 120 and 200 C. The results revealed that the hydrogenation kinetics is of the order 0.5-2 with respect to hydrogen and that the reaction order increases with temperature. The reaction order with respect to toluene increases from slightly negative values to zero order over the temperature domain studied. The kinetics was modeled with an empirical power-law rate expression and with two mechanistic rate models. The latter models were based on the assumption of rapid competitive adsorption steps of toluene and hydrogen and rate-determining surface reaction steps involving addition of hydrogen atom pairs to adsorbed toluene and partially hydrogenated intermediate molecules. The surface coverages, the activation energy, and the optimal reaction temperature giving the maximum reaction rate were estimated using parameter values obtained from one of the mechanistic models.