Does H₂ Temperature-Programmed Reduction Always Probe Solid-State Redox Chemistry? The Case of Pt/CeO₂

Redox reactions on the surface of transition metal oxides are of broad interest in thermo, photo, and electrocatalysis. H₂ temperature-programmed reduction (H₂-TPR) is commonly used to probe oxide reducibility by measuring the rate of H₂ consumption during temperature ramps, assuming that this rate is controlled by oxide reduction. However, oxide reduction involves several elementary steps, such as H₂ dissociation and H-spillover, before surface reduction and H₂O formation occur. In this study, we evaluated the kinetics of H₂ consumption over CeO₂ and Pt/CeO₂ with varying Pt loadings and structures to identify the elementary steps probed by H₂-TPR. Literature often attributes changes in H₂-TPR characteristics with Pt addition to increased CeO₂ reducibility. However, our analysis revealed that the H₂ consumption rate is measurement of the rate of H-spillover at Pt-CeO₂ interfaces and is determined by the concentration of Pt species on Pt nanoclusters that dissociate H₂. Therefore, lower temperature H₂ consumption observed with Pt addition does not indicate higher CeO₂ reducibility. Measurements on samples with mixtures of Pt single-atoms and nanoclusters demonstrated that H₂-TPR can effectively quantify dilute Pt nanocluster concentrations, suggesting caution in directly linking H₂-TPR characteristics to oxide reducibility while highlighting alternative material insights that can be gleaned.