Selective formation of alkenes through the cracking of n-heptane on Ca2+-exchanged ferrierite

The cracking of n-heptane was carried out as a model reaction of naphtha cr acking by using various zeolite catalysts to obtain light alkenes. such as ethylene. propylene and butenes. with high selectivity at high conversion l evels. The selectivity of zeolites having pore openings of 10 and 12-member ed rings was compared at 80% conversion. H-ZSM-5 and H-ferrierite gave high er alkene selectivity than H-MCM-22. H-mordenite. H-beta and H-Y. The effec t of exchanged cations on the alkene selectivity was also examined with H-Z SM-5 and H-ferrierite. Ca2+ or Ba2+-exchanged ferrierite gave the highest s electivity to alkenes, 60 C-% at 70%; conversion. The Ca2+-exchange effecti vely suppressed the secondary hydride transfer that would consume alkenes t o form hydrogen-deficient species. As a result, the coke formation from the hydrogen deficient species was also suppressed on Ca2+-exchanged ferrierit e. which did not exhibit the rapid deactivation with time-on-stream. (C) 20 01 Elsevier Science B.V. All rights reserved.