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

초록

Redox reactions on the surface of transition metal oxides are of broad interest in thermo, photo, and electrocatalysis. H-2 temperature-programmed reduction (H-2-TPR) is commonly used to probe oxide reducibility by measuring the rate of H-2 consumption during temperature ramps, assuming that this rate is controlled by oxide reduction. However, oxide reduction involves several elementary steps, such as H-2 dissociation and H-spillover, before surface reduction and H2O formation occur. In this study, we evaluated the kinetics of H-2 consumption over CeO2 and Pt/CeO2 with varying Pt loadings and structures to identify the elementary steps probed by H-2-TPR. Literature often attributes changes in H-2-TPR characteristics with Pt addition to increased CeO2 reducibility. However, our analysis revealed that the H-2 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 H-2. Therefore, lower temperature H-2 consumption observed with Pt addition does not indicate higher CeO2 reducibility. Measurements on samples with mixtures of Pt single-atoms and nanoclusters demonstrated that H-2-TPR can effectively quantify dilute Pt nanocluster concentrations, suggesting caution in directly linking H-2-TPR characteristics to oxide reducibility while highlighting alternative material insights that can be gleaned.

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