How Pt Influences H2 Reactions on High Surface-Area Pt/CeO2 Powder Catalyst Surfaces

The addition of platinum-groupmetals (PGMs, e.g., Pt) to CeO2 is used in heterogeneouscatalysis to promote the rate ofredox surface reactions. Well-defined model system studies have shownthat PGMs facilitate H-2 dissociation, H-spillover ontoCeO(2) surfaces, and CeO2 surface reduction. However,it remains unclear how the heterogeneous structures and interfacesthat exist on powder catalysts influence the mechanistic picture ofPGM-promoted H-2 reactions on CeO2 surfaces developedfrom model system studies. Here, controlled catalyst synthesis, temperature-programmedreduction (TPR), in situ infrared spectroscopy (IR), and in situ electronenergy loss spectroscopy (EELS) were used to interrogate the mechanismsof how Pt nanoclusters and single atoms influence H-2 reactionson high-surface area Pt/CeO2 powder catalysts. TPR showedthat Pt promotes H-2 consumption rates on Pt/CeO2 even when Pt exists on a small fraction of CeO2 particles,suggesting that H-spillover proceeds far from Pt-CeO2 interfaces and across CeO2-CeO2 particleinterfaces. IR and EELS measurements provided evidence that Pt changesthe mechanism of H-2 activation and the rate limiting stepfor Ce3+, oxygen vacancy, and water formation as comparedto pure CeO2. As a result, higher-saturation surface hydroxylcoverages can be achieved on Pt/CeO2 compared to pure CeO2. Further, Ce3+ formed by spillover-H from Pt isheterogeneously distributed and localized at and around interparticleCeO(2)-CeO2 boundaries, while activatedH(2) on pure CeO2 results in homogeneously distributedCe(3+). Ce3+ localization at and around CeO2-CeO2 boundaries for Pt/CeO2 isaccompanied by surface reconstruction that enables faster rates ofH(2) consumption. This study reconciles the materials gapbetween model structures and powder catalysts for H-2 reactionswith Pt/CeO2 and highlights how the spatial heterogeneityof powder catalysts dictates the influence of Pt on H-2 reactionsat CeO2 surfaces.