Metal zeolite catalysts are crucial for a wide-range of commercially relevant processes with
Cu-SSZ-13 notably being employed for the NOx abatement of automotive exhausts. However,
the speciation of these metal sites is dependent on the ion-exchange procedure during the
catalyst’s synthesis with the atomistic ion-exchange mechanism of transition metals into
zeolites remaining elusive. Therefore, this work presents a novel scheme for modelling the
migration of metal complexes with explicit hydration, evaluated at the quantum mechanical
level in a computationally tractable manner, referred to as partial relaxation-geometry
optimisation (PRGO). From this, exhaustive pro les of mass transfer in the bulk crystal
and (001) surface of CHA for a range of divalent metals along with their accessible spin states
have been modelled. From these migrations, it was found that FeII unexpectedly undergoes
a reduction in spin from M = 5 to M = 3 as it migrates between the cages as well as
the transition state for CoII being predicted to have a degenerate spin preference in the bulk
crystal. Moreover, a supervised machine-learning procedure has been developed, referred to as
optimal feature nder with optional functional variance (OFF-OFV), that has been employed
to determine the key features and thermodynamic drives of these migrations. Additionally,
experimental work coupled with these PRGO and OFF-OFV methods demonstrates that
the rate-limiting step for ion-exchange is surface mediated with a tentative mechanism
being presented for the uptake of metals from the external solution to the CHA zeolite.
Finally, a high-throughput work
ow for generating expanded valence framework Al species
has been developed for a range of topologies where examination of these structures has
demonstrated that MOR exhibits a T-site preference for forming 5-fold structures, which
causes framework cleavage to become exothermic. Therefore, these Al framework sites with
additional coordination will form selectively within the MOR crystal and introduce weakness
into the framework, resulting in additional defects being present that will inevitably a ect
catalysis. This work presents a range of novel methods to examine a vast array of industrially
relevant zeolite systems in a tractable manner to provide unique insight into the ion-exchange
mechanism and the zeolite structure which would be unattainable without the approaches
developed here.