Effects of the nature of coke on the activity and stability of the hybrid catalyst used in the aromatization of ethylene and n-butane Original Research Article

In the aromatization of light hydrocarbons, hybrid catalysts containing Zn or Ga supported co-catalysts showed much better performance and on-stream stability than the parent ZSM-5 zeolite. This was attributed to the beneficial effect of the co-catalyst on the nature of the coke formed in the zeolite particles. In fact, with both Zn and Ga hybrid catalyst systems, it was observed that the coke species formed were ‘light’ coke having a paraffinic nature, in contrast with the more aromatic ‘heavy’ coke produced by the parent zeolite. Particularly with n-butane feed, it was the nature of the coke formed which determined the activity and stability of the catalyst since both catalysts produced nearly equal amounts of coke under the same reaction conditions. As a general result of this study, the lighter the coke formed, the more aromatic the product stream and the higher the on-stream catalyst stability.