17O-EPR determination of the structure and dynamics of copper single-metal sites in zeolites

The bonding of copper ions to lattice oxygens dictates the activity and selectivity of copper exchanged zeolites. By O-17 isotopic labelling of the zeolite framework, in conjunction with advanced EPR methodologies and DFT modelling, we determine the local structure of single site Cu-II species, we quantify the covalency of the metal-framework bond and we assess how this scenario is modified by the presence of solvating (H2O)-O-16 or (H2O)-O-17 molecules. This enables to follow the migration of Cu-II species as a function of hydration conditions, providing evidence for a reversible transfer pathway within the zeolite cage as a function of the water pressure. The results presented in this paper establish O-17 EPR as a versatile tool for characterizing metal-oxide interactions in open-shell systems. The identification of catalytically active sites with atomic-scale precision occupies a central place in the theory and practice of heterogeneous catalysis. Here the authors assess the nature of the copper-oxygen bond in a Cu-CHA zeolite and recover the microscopic structure of single-metal sites.