Electronic and Geometric Structure of Copper Single-Metal Sites in Zeolites by Hyperfine Spectroscopy and Quantum Chemical Modelling

A Thesis submitted to the Universities of Leipzig and Turin in candidature for a Joint PhD degree by Paolo Cleto Bruzzese

Abstract
Atomically dispersed transition metal ions in zeolites catalyse a wide range of
industrial reactions and are at the centre of intense research interest to design
new sustainable synthetic pathways for energy conversion and environment remediation.
One of the big challenges in this context is the characterization and
location of the active sites. Indeed, mapping their nature with atomic-scale
precision occupies a central place in the theory and practice of heterogeneous
catalysis.
In this thesis, the site-selectivity and sensitivity of Electron Paramagnetic
Resonance (EPR) with its pulsed variants are combined with quantum chemical
modelling to determine the microscopic structure of monomeric CuII species in
zeolites with Chabazite (CHA) topology as a function of the hydration conditions
and sample composition. By isotopic labelling of the zeolite framework
with 17O and employing 17O ENDOR spectroscopy, the degree of covalency in
the Cu-O bond is mapped and the evolution of CuII sites as a function of the
hydration conditions is followed. By combining 1H HYSCORE experiments with
state-of-the-art quantum chemical modelling, the EPR signature of the redox active
hydroxo-CuII species is univocally identified and a quantitative assessment
of its electronic and geometric structureis provided as a function of zeolite composition.