Structure and reactivity of surface oxides on Cu(100)

Abstract: Adsorption of oxygen onto Cu(100) leads to formation of a well-ordered surface structure known as the `missing row' (MR) reconstruction. The aim of the work described in this thesis was to characterize the chemical properties of this MR structure, which serves as a well-defined analogue for oxidized copper surfaces used in catalysis for CO2 hydrogenation. Specifically, the interaction of CO2 with the MR structure has been studied and compared measurements on the bare Cu(100) surface and on a partially-reduced MR surface prepared by exposure to H2. The results show that the reduction of the MR structure initially takes place at the lower terraces adjacent to step edges and at defects, producing a new phase which appears to have an amorphous structure. XPS results show a new oxygen species appearing upon reduction, which is attributed to this new structure. The XPS data further show that CO2 sticks more strongly on the oxygen-rich surfaces than on clean Cu(100), though CO2 adsorbs dissociatively on clean Cu(100) and the reduced MR surface, but not on the pure MR structure. Preliminary catalytic tests using an in-situ flow reactor showed conversion of CO2 to CO above 650 C, although the signal was weak. These results demonstrate the feasibility of further experiments using this cell for in-situ surface x-ray diffraction experiments to be conducted in the future.