Selectivity and Deactivation Profiles of Zeolite Type Materials in the MTO Process

The reaction of methanol to olefins was studied over the following zeolite type materials: ZSM-5, SAPO-34 and chabazite (mineral). A strongly shape-selective catalyst (8-ring channels) is needed to suppress the formation of aromatics, and thereby get the highest olefin selectivity. Olefin yields slightly above 80 mol% at close to 100% conversion could be obtained with the H-SAPO-34 catalyst. Fast deactivation is the main limitation in the MTO reaction. The deactivation rate, which was much smaller in the case of H-ZSM-5 catalysts, appears partly structure dependent, but a large difference in deactivation rate between the isostructural catalysts chabazite and SAPO-34 was observed. Temperature programmed desorption of ammonia showed the chabazite and ZSM-5 to contain acid sites with higher acidity than is found in SAPO-34. The acid site content varies as follows: H-chabazite > SAPO-34 > H-ZSM-5.