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 O2 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.