How Pt Influences H Reactions on High Surface-Area Pt/CeO Powder Catalyst Surfaces.

The addition of platinum-group metals (PGMs, e.g., Pt) to CeO is used in heterogeneous catalysis to promote the rate of redox surface reactions. Well-defined model system studies have shown that PGMs facilitate H dissociation, H-spillover onto CeO surfaces, and CeO surface reduction. However, it remains unclear how the heterogeneous structures and interfaces that exist on powder catalysts influence the mechanistic picture of PGM-promoted H reactions on CeO surfaces developed from model system studies. Here, controlled catalyst synthesis, temperature-programmed reduction (TPR), in situ infrared spectroscopy (IR), and in situ electron energy loss spectroscopy (EELS) were used to interrogate the mechanisms of how Pt nanoclusters and single atoms influence H reactions on high-surface area Pt/CeO powder catalysts. TPR showed that Pt promotes H consumption rates on Pt/CeO even when Pt exists on a small fraction of CeO particles, suggesting that H-spillover proceeds far from Pt-CeO interfaces and across CeO-CeO particle interfaces. IR and EELS measurements provided evidence that Pt changes the mechanism of H activation and the rate limiting step for Ce, oxygen vacancy, and water formation as compared to pure CeO. As a result, higher-saturation surface hydroxyl coverages can be achieved on Pt/CeO compared to pure CeO. Further, Ce formed by spillover-H from Pt is heterogeneously distributed and localized at and around interparticle CeO-CeO boundaries, while activated H on pure CeO results in homogeneously distributed Ce. Ce localization at and around CeO-CeO boundaries for Pt/CeO is accompanied by surface reconstruction that enables faster rates of H consumption. This study reconciles the materials gap between model structures and powder catalysts for H reactions with Pt/CeO and highlights how the spatial heterogeneity of powder catalysts dictates the influence of Pt on H reactions at CeO surfaces.