Unveiling the CO Oxidation Mechanism over a Molecularly Defined Copper Single-Atom Catalyst Supported on a...

Elucidating the reaction mechanism in heterogeneous catalysis is critically important for catalyst development, yet remains challenging because of the often unclear nature of the active sites. Using a molecularly defined copper single-atom catalyst supported by a UiO-66 metal-organic framework (Cu/UiO-66) allows a detailed mechanistic elucidation of the CO oxidation reaction. Based on a combination of in situ/operando spectroscopies, kinetic measurements including kinetic isotope effects, and density-functional-theory-based calculations, we identified the active site, reaction intermediates, and transition states of the dominant reaction cycle as well as the changes in oxidation/spin state during reaction. The reaction involves the continuous reactive dissociation of adsorbed O₂ , by reaction of O_2,ad with CO_ad , leading to the formation of an O atom connecting the Cu center with a neighboring Zr⁴⁺ ion as the rate limiting step. This is removed in a second activated step.