Extraframework transition metal ions (TMIs) in zeolites
can serve
as active sites for adsorption and catalysis. However, due to the
complexity and mobility of extraframework cation sites, their applications
are significantly limited and the structure–performance relationship
is poorly understood. In this Perspective, stable and uniform TMIs
in zeolites are exemplified and their characteristics are discussed.
A series of TMIs can be introduced to specific cation sites of faujasite via a ligand-protected in situ synthesis
route to construct uniform TMIs in the zeolite matrix, namely, TMI@FAU
(TMI= Co, Ni, Cu, Rh, and Pt). Coordinatively unsaturated TMIs within
faujasite are active for small-molecule adsorption and activation,
and therefore, TMI@FAU zeolites show unique properties in adsorption
and catalysis. TMI@FAU zeolites appear to be ideal model systems,
and the well-defined structure of TMI@FAU greatly facilitates the
mechanism studies by spectroscopic investigations and theoretical
simulations.