Unveiling the Role and Stabilization Mechanism of Cu⁺ into Defective Ce-MOF Clusters during CO Oxidation

Copper single-site catalysts supported on Zr-based metal-organic frameworks (MOFs) are well-known systems in which the nature of the active sites has been deeply investigated. Conversely, the redox chemistry of the Ce-counterparts is more limited, because of the often-unclear Cu²⁺/Cu⁺ and Ce⁴⁺/Ce³⁺ pairs behavior. Herein, we studied a novel Cu²⁺ single-site catalyst supported on a defective Ce-MOF, Cu/UiO-67(Ce), as a catalyst for the CO oxidation reaction. Based on a combination of in situ DRIFT and operando XAS spectroscopies, we established that Cu⁺ sites generated during catalysis play a pivotal role. Moreover, the oxygen vacancies associated with Ce³⁺ sites and presented in the defective Cu/UiO-67(Ce) material are able to activate the O₂ molecules, closing the catalytic cycle. The results presented in this work open a new route for the design of active and stable single-site catalysts supported on defective Ce-MOFs.