Preferential oxidation (PrOx) of CO is a promising energy efficient alternative to CO methanation for purifying H2 streams from steam reforming processes. With high-purity H2 being the desired product, the obvious challenge is to find a catalyst that readily oxidizes CO, but does not burn H2. Through integrated experimental and computational studies we have produced evidence suggesting that O2 and H2 activation over Au/TiO2 catalysts occurs at the metal-support interface (MSI).1,2 The activation of O2 on Au is assisted by support protons originating from hydroxyl groups or weakly adsorbed water molecules. In contrast, H2 dissociation across the MSI occurs heterolytically resulting in a Au-hydride and a proton on the oxide support. The accessibility and strength of proton accepting/donating sites on the titania support can be tuned by controlling the amount of water in the reaction feed. Water adsorbs weakly on the titania support and near the MSI, where it increases the local proton concentration. This is beneficial for O2 activation and, in turn, for CO oxidation on Au. Conversely, the increased proton concentration and the screening of basic support sites by water impede the heterolytic H2 activation at the MSI. Given the opposing effect of water on CO and H2 oxidation it is possible to achieve very high PrOx selectivity with standard supported Au catalysts by simply tuning the partial pressure of water and maintaining ca. 1 monolayer of weakly adsorbed water on the support.

How water improves the selectivity of preferential oxidation of CO in the presence of excess H2 over Au/TiO2

2019 Fall National Meeting

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