(348a) Investigations of Surface Chemistry for Pyridine-Catalyzed CO2 Reduction on Gallium Phosphide
Two recent highlights from these studies will be discussed. First, we report on a combined investigation through experiment and theory on the surface-bound species on GaP(110) formed upon interaction with water. Experimentally, surface-bound species over 10 orders of magnitude of pressure were spectroscopically identified in situ using synchrotron-based ambient pressure photoelectron spectroscopy (APPES). Ga3d and O1s core-level spectra indicate that the interaction of GaP(110) with H2O induces formation of a partially dissociated adlayer, characterized by the presence of both Gaâ??OH and molecular H2O species. Measurements of the P2p core level indicate formation of a negatively charged hydride that irreversibly bonds to surface P in vacuum. The surface densities of the hydroxide and hydride species increase with increasing pressure (surface coverage) of water. Isobaric measurements at elevated pressures were used to probe the thermal stabilities of adsorbed species as well as the oxidation of surface Ga and P. The observation of stable surface hydride formation induced by interaction with water is especially notable given the critical role of hydride transfer to catalysts and CO2 during chemical fuel synthesis reactions in aqueous environments. Secondly, we describe a scanning tunneling microscopy (STM) and density functional theory investigation of the orbital-resolved adsorption state defining the dative bonding interaction between a GaP(110) surface and a N-containing heteroaromatic (pyridine).Â By examining the distribution of unoccupied molecular orbitals, we show that STM images can be used to positively identify the sites on pyridine susceptible to nucleophilic attack, consistent with frontier orbital theory. This indicates that STM can be used to explore the local reaction centers of adsorbed ambidentate electrophiles and nucleophiles relevant to artificial photosynthesis, and more broadly to generate critical mechanistic information for various heterogeneous acidâ??base reactions.