Atomic-Scale Insights into Cu-Modified ZrO2 Catalysts: The Crucial Role of Surface Clusters in Phenol Carboxylation with CO2

The catalytic performance of metal oxide materials is profoundly influenced by both chemical composition and surface morphology, particularly at high dopant loadings where metallic clusters can form. Here, we use density functional theory (DFT) to elucidate how copper incorporation—either as isolated dopants or as surface clusters—modulates the mechanism and activity of ZrO2 catalysts in the direct carboxylation of phenol to para-hydroxybenzoic acid. Our results reveal that while Cu doping inhibits C–H bond activation, the presence of Cu clusters at the ZrO2 surface dramatically lowers the barrier for C–C coupling with CO2, owing to unique interfacial sites that facilitate substrate activation and CO2 bending. We show that the reaction mechanism shifts from an Eley–Rideal pathway on pure ZrO2 to a Langmuir–Hinshelwood mechanism on Cu-modified surfaces, with the rate-determining step depending on the Cu morphology. These findings demonstrate that even small amounts of metallic clusters can fundamentally alter catalytic pathways, providing actionable insights for the rational design of heterogeneous catalysts for selective aromatic carboxylation.