Shape-selective catalysis in cavity-type molecular sieves: cavity-controlled catalytic principle.

The methanol-to-olefins (MTO) process, driven by zeolites or molecular sieves, a cornerstone of C1 chemistry, has established a substantial pathway for generating olefin products from non-petroleum sources. Molecular sieves exhibit significant benefits in catalysis with shape selectivity due to the unique confinement environment and acidic properties, featuring their molecular sieving and confinement effects. Significantly, eight-membered ring (8-MR) and cavity-type molecular sieve catalysts, characterized by large cage volumes and restricted window openings, exhibit distinctive host-guest interactions between the cavity structure and the reactants, intermediates, and products within the confined space, thereby revealing the cavity-controlled methanol conversion principle in molecular adsorption and diffusion, intermediate formation, reaction pathway, and catalyst deactivation processes. This review mainly summarizes molecular adsorption characteristics and diffusion behavior, as well as the mechanisms of the MTO reaction and catalyst deactivation within cavity-type molecular sieves. A comprehensive introduction is provided on the variations in preferential adsorption sites and diffusion behavior of guest molecules induced by different cavity structures within cavity-type molecular sieves. Furthermore, the critical intermediate generation governed by cavity structure and the nonuniform distribution of coke species within the catalyst were also discussed. The cavity-controlled catalytic principle of the MTO reaction driven by 8-MR and cavity-type molecular sieves provides valuable insights for the modification of molecular sieve catalysts and the optimization of the MTO process and also promotes broader application of these catalysts in other C1 chemical reactions.