Inverse Catalysts for CO Oxidation: Enhanced Oxide-Metal Interactions in MgO/Au(111), CeO2/Au(111), and TiO2/Au(111)

Au(111) does not bind CO and O-2 well. The deposition of small nanoparticles of MgO, CeO2, and TiO2 on Au(111) produces excellent catalysts for CO oxidation at room temperature. In an inverse oxide/metal configuration there is a strong enhancement of the oxide-metal interactions, and the inverse catalysts are more active than conventional Au/ MgO(001), Au/CeO2(111), and Au/TiO2(110) catalysts. An identical trend was seen after comparing the CO oxidation activity of TiO2/Au and Au/TiO2 powder catalysts. In the model systems, the activity increased following the sequence: MgO/Au(111) < CeO2/Au(111) < TiO2/Au(111). Ambient pressure X-ray photoelectron spectroscopy (AP-XPS) was used to elucidate the role of the titania-gold interface in inverse TiO2/Au(111) model catalysts during CO oxidation. Stable surface intermediates such as CO(ads), CO32- (ads), and OH(ads) were identified under reaction conditions. CO32- (ads) and OH(ads) behaved as spectators. The concentration of CO(ad) initially increased and then decreased with increasing TiO2 coverage, demonstrating a clear role of the Ti-Au interface and the size of the TiO2 nanostructures in the catalytic process. Overall, our results show an enhancement in the strength of the oxide-metal interactions when working with inverse oxide/metal configurations, a phenomenon that can be utilized for the design of efficient catalysts useful for green and sustainable chemistry.