A comparative study of methanol to olefin over CHA and MTF zeolites

H-SSZ-13 (CHA) and H-UTM-1 (MTF) zeolites have been synthesized, characterized, and employed as catalysts for the methanol-to-olefin (MTO) reaction. Both zeolites have eight-membered rings, and their structures and acidities are characterized by Al-27 magic-angle spinning (MAS) NMR, NH3-TPD (temperature-programmed desorption), and in-situ IR spectroscopy. In-situ IR spectroscopy indicates that methanol is efficiently activated on the Bronsted acid sites of both zeolites. At 673 K, the methanol is quantitatively converted to hydrocarbons, mainly ethene and propene, over H-SSZ-13, whereas H-UTM-1 only initially gives a small amount of alkenes, the main product being dimethyl ether. It is proposed that the limited space in the cages of the MTF zeolite prevents formation of intermediate polymethylbenzenes and thereby also formation of hydrocarbons, whereas the cage size in the CHA type zeolite, which is active, is large enough to accommodate polymethylbenzenes.