Toluene Disproportionation and Coke Formation on Mordenites Effect of Catalyst Modifications and of Operating Conditions

Abstract

Improving catalytic stability of mordenite has been attempted by using three types of treatment: dealumination, wet air heating, nickel-ion-exchange. The rates of disproportionation and coking on these samples have been compared under different operating conditions: low and high hydrogen or nitrogen pressures. Under nitrogen, mordenite deactivation is very fast. Dealumination increases its activity for disproportionation and coking as well as the deactivation rate, while wet air treatment decreases its coking activity. This decrease may be connected with the elimination of Brönsted acid sites. The catalytic stability of all samples is considerably improved by operating under high hydrogen pressure, the best catalyst being the wet air treated nickel-exchanged mordenite. This stabilizing effect of hydrogen is the result of coking inhibition and of a better distribution of coke in the bulk of the catalyst pellet than under nitrogen. It is suggested that coking inhibition comes from the presence on mordenite of sites capable of activating molecular hydrogen.