Unlocking the potential for pseudo-molecular catalysts via understanding the activity of transition metal ionic species in zeolites

Abstract

Transition metal ions (TMIs) hosted in zeolites have potential for generating highly active and selective catalysts. The speciation of metal ions inside the microporous zeolite pore system, including geometric constraints and anchoring points, grouping, and nuclearity of species, is not well understood. Determination of the location and structure of active sites is challenging because different species co-exist in the same zeolite, and complexity is added by their dynamics under reaction conditions. Three parameters are influential on the speciation of active TMIs in zeolites: (1) zeolite properties, including framework structure, composition, and metal loadings; (2) mobility of TMI species inside the zeolite micropores; and (3) influence of other inorganic species present in the reaction spaces. In our view, molecular-level understanding of metal-ion-exchanged zeolite catalysts requires a set of characterization and computational techniques that should go hand in hand with refined synthetic methods selectively generating active species.