Water Poisons H2 Activation at the Au-TiO2 Interface by Slowing Proton and Electron Transfer between Au and Titania.

Understanding the dynamic changes at the active site during catalysis is a fundamental challenge that promises to improve catalytic properties. While performing Arrhenius studies during H2 oxidation over Au/TiO2 catalysts, we found different apparent activation energies (Eapp) depending on the feed water pressure. This is partially attributed to changing numbers of metal-support interface (MSI) sites as water coverage changes with temperature. Constant water coverage studies showed two kinetic regimes: fast heterolytic H2 activation directly at the MSI (Eapp ~25 kJ/mol) and significantly slower heterolytic H2 activation mediated by water (Eapp ~45 kJ/mol). The two regimes had significantly different kinetics, suggesting a complicated mechanism of water poisoning. Density functional theory (DFT) showed water has minor effects on the reaction thermodynamics, primarily attributable to intrinsic differences in surface reactivity of different Au sites in the DFT model. The DFT model suggested significant surfa...