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 cracking by using various zeolite catalysts to obtain light alkenes. such as ethylene. propylene and butenes. with high selectivity at high conversion levels. The selectivity of zeolites having pore openings of 10 and 12-membered rings was compared at 80% conversion. H-ZSM-5 and H-ferrierite gave higher alkene selectivity than H-MCM-22. H-mordenite. H-beta and H-Y. The effect of exchanged cations on the alkene selectivity was also examined with H-ZSM-5 and H-ferrierite. Ca2+ or Ba2+-exchanged ferrierite gave the highest selectivity to alkenes, 60 C-% at 70%; conversion. The Ca2+-exchange effectively suppressed the secondary hydride transfer that would consume alkenes to form hydrogen-deficient species. As a result, the coke formation from the hydrogen deficient species was also suppressed on Ca2+-exchanged ferrierite. which did not exhibit the rapid deactivation with time-on-stream. (C) 2001 Elsevier Science B.V. All rights reserved.