Reactivation of coked H-ZSM-5 by treatment with hydrogen and alkanes

The conversion of methanol to hydrocarbons on zeolite H-ZSM-5, in particular the long-term stability of the catalyst, was studied under different reaction conditions, Whereas no significant change in the product distribution was observed, hydrogen and alkane-containing recycle gases show lower deactivation rates than nitrogen, In addition, spent catalysts were partially reactivated by alkane treatment, increasing the time on stream before an oxidative regeneration procedure is required, Lower alkanes such as propane and isobutane yield the best results. The influence of hydrogen-containing gases on the deactivation rate and on the nature of coke on zeolite H-ZSM-5 indicates dissociative adsorption of hydrogen and alkanes on a few sites with enhanced activity. Surface hydrogen species formed by adsorption of alkanes are assumed to make possible the hydrocracking of carbonaceous deposits. (C) 1996 Academic Press, Inc.