Catalytic cracking of propane over impregnated mesoporous ZSM-5: A strategy to change product distribution by sequential modification

ZSM-5 was subjected to two different modifications, namely mesopore creation with 0.2 m NaOH and metal impregnation with 10 wt% of La or Cu, with particular emphasis on the sequence of these modifications. Alkali treatment of ZSM-5 led to extraction of silica and alumina, resulted in loss of strong acid sites, and enhanced accessibility. Furthermore, acidity could be regulated by impregnation with metals. High olefin selectivity (68%), optimal propylene to ethylene ratio (P/E = 1.20), and reasonable stability were obtained over a catalyst produced by a Desilication–Impregnation Sequence (DIS) (AT-10La-ZSM-5). Modification of ZSM-5 by reverse Impregnation–Desilication Sequence (IDS) decreased selectivity, considerably. The modification sequence thus appears to be a key factor in determining the product distribution, and we propose that it may provide a facile new method to control the reaction path.