Dynamic modification of pore opening of SAPO-34 by adsorbed surface methoxy species during induction of catalytic methanol-to-olefins reactions

摘要

Here, we report that the 8-membered ring pore opening of SAPO-34 zeolite can be significantly modified by an adsorbed surface methoxy species (SMS) during the induction period of the catalytic methanol-to-olefins process, which offers molecular sieving properties. It is due to the physical obstruction caused by the surface methoxy species, which also modifies the adsorption properties of other hydrocarbons. Synchrotron X-ray powder diffraction and Rietveld refinement reveal that the SMS is dynamically created from methanol dehydration on a Bronsted acid site near the narrow pore windows. Thus, industrially desirable lower olefins such as ethylene and propylene can be favourably made at the expense of higher olefins. The crystal structures and fundamental understanding in altering the olefin selectivity during induction may allow rational optimisation in catalytic performance under complex fluidised conditions. This work offers additional but alternative insights to the 'dual cycle' mechanistic study of the catalytic methanol-to-olefins process.