Facet-Dependent Regulation of Reactive Oxygen Species Generation and Utilization Governs Biomass Oxidation

Reactive oxygen species (ROS) are key intermediates in radical-mediated heterogeneous oxidation, yet the relationship between ROS generation and their effective utilization remains poorly understood. Here, we demonstrate that crystal facets can differently influence ROS generation and utilization during biomass-derived alcohol/aldehyde oxidation. Using CuO catalysts, predominantly exposing either the (001) or (111) facet as model systems, we show that the CuO(001) facet preferentially promotes hydroxyl radical (·OH) generation through efficient tert-butyl hydroperoxide activation, whereas the CuO(111) facet promotes efficient interfacial utilization of surface-associated ·OH during the hydrogen-abstraction step. Despite producing fewer EPR-detectable radicals, CuO(111) exhibits higher catalytic performance for the base-free oxidation of 5-hydroxymethylfurfural to 2,5-furandicarboxylic acid, achieving quantitative HMF conversion and an FDCA yield of 85.7% under mild conditions (80 °C, 4 h). Time-resolved kinetic analysis, radical trapping experiments, electron paramagnetic resonance spectroscopy, and density functional theory calculations reveal that facet-dependent adsorption configurations regulate oxidant activation and subsequent hydrogen abstraction, thereby determining whether generated ROS undergo productive interfacial reactions or non-productive accumulation. This work provides mechanistic insights into the relationship between ROS generation, ROS utilization, and catalytic performance, highlighting the importance of considering the productive participation of generated ROS in catalyst evaluation.