CATALYST DEACTIVATION DURING THE HYDROGENATION OF BENZENE OVER NICKEL-LOADED Y-ZEOLITES

The hydrogenation of benzene to cyclohexane was investigated over a range of nickel-exchanged and nickel-impregnated Y zeolites, varying the nickel content and the nature of the alkali metal co-cation (Li+, Na+, K+, Rb+ or Cs+). With a view to optimizing benzene conversion levels, the following catalytic parameters were studied: reaction temperature, reaction time, benzene flow rate and coke deposition. The observed catalytic activities are correlated with previously reported physical characterizations. Benzene hydrogenation increased in the order: NiLiY < NiNaY < NiKY < NiRbNaY < NiCsNaY. Catalyst deactivation results from the deposition of involatile coke on the catalyst surface, which is promoted by increasing zeolite acidity. The effects of poisoning the surface Bronsted acid sites by adsorption of ammonia onto the activated reduced zeolites are considered. The results of catalyst regeneration by high temperature oxidation of the coke deposits are also reported.