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 cat- alysts. The speciation of metal ions inside the microporous zeolite pore system, including geometric con- straints 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 influen- tial on the speciation of active TMIs in zeolites: (1) zeolite properties, including framework structure, compo- sition, 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.