Methanol-to-olefin conversion over H-MCM-22 and H-ITQ-2 zeolites

The methanol-to-olefin (MTO) performance of H-MCM-22 and H-ITQ-2, as well as of their dealuminated analog prepared via oxalic acid treatment, is compared with the catalytic behavior of H-ZSM-5 and H-SAPO-34. The contribution of two-dimensional sinusoidal 10-ring channels in H-MCM-22 to the overall catalytic action of this medium-pore zeolite, especially to the propene selectivity, was found to be considerably greater than that of its cylindrical supercages, probably due to the smaller void volume and hence to the higher concentration of intrazeolitic reactant molecules. Despite the much larger cage volume (480 vs. 240 Å3), H-MCM-22 shows a much slower deactivation rate than H-SAPO-34. A similar result, although less pronounced, can be observed when compared to the channel-based H-ZSM-5 zeolite with a slightly lower Si/Al ratio (14). The overall results of our study demonstrate that not only the pore architecture (cage-based vs. channel-based pore systems) of zeolitic materials but also the properties (density, strength, and location) of their acid sites are a critical factor governing the MTO selectivity and stability.