Role of Alkali Metal Promoter in Zeolite-Encapsulated Subnanometer Metal Catalysts

Zeolite-supported metal catalysts are gaining importance due to their use in current industrial processes and their promising applications in emerging reactions. Recent advancements in synthesis and characterization have enabled the creation of subnanometer metal active sites with controlled sizes and locations within zeolites, offering better performance than traditional metal catalysts supported on carbon or oxide carriers. Recent studies show that alkali promoters play a crucial role in stabilizing isolated metal atoms and subnanometer clusters in zeolites, preventing them from sintering into nanoparticles. Moreover, alkali metals also influence catalytic properties, as reflected in the modulation of product distribution and catalyst regenerability. In this Perspective article, we will discuss a plausible mechanism by which alkali metals stabilize metal sites in zeolite structures, supported by experimental characterization and theoretical calculations. By elucidating the role of alkali metal promoters in some typical catalytic reactions, we aim to achieve a unified understanding of the role of alkali promoters in tuning the coordination environment and chemical reactivity of subnanometer metal species in zeolites, which may guide the design of synthesis strategies for zeolite-encapsulated subnanometer metal catalysts for industrially relevant reactions.