How Pt Influences H 2 Reactions on High Surface-Area Pt/CeO 2 Powder Catalyst Surfaces.

The addition of platinum-group metals (PGMs, e.g., Pt) to CeO 2 is used in heterogeneous catalysis to promote the rate of redox surface reactions. Well-defined model system studies have shown that PGMs facilitate H 2 dissociation, H-spillover onto CeO 2 surfaces, and CeO 2 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 2 reactions on CeO 2 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 2 reactions on high-surface area Pt/CeO 2 powder catalysts. TPR showed that Pt promotes H 2 consumption rates on Pt/CeO 2 even when Pt exists on a small fraction of CeO 2 particles, suggesting that H-spillover proceeds far from Pt-CeO 2 interfaces and across CeO 2 -CeO 2 particle interfaces. IR and EELS measurements provided evidence that Pt changes the mechanism of H 2 activation and the rate limiting step for Ce 3+ , oxygen vacancy, and water formation as compared to pure CeO 2 . As a result, higher-saturation surface hydroxyl coverages can be achieved on Pt/CeO 2 compared to pure CeO 2 . Further, Ce 3+ formed by spillover-H from Pt is heterogeneously distributed and localized at and around interparticle CeO 2 -CeO 2 boundaries, while activated H 2 on pure CeO 2 results in homogeneously distributed Ce 3+ . Ce 3+ localization at and around CeO 2 -CeO 2 boundaries for Pt/CeO 2 is accompanied by surface reconstruction that enables faster rates of H 2 consumption. This study reconciles the materials gap between model structures and powder catalysts for H 2 reactions with Pt/CeO 2 and highlights how the spatial heterogeneity of powder catalysts dictates the influence of Pt on H 2 reactions at CeO 2 surfaces.