MgO Nanostructures on Cu(111): Understanding Size- and Morphology-Dependent CO2 Binding and Hydrogenation

To design and optimize cost-effective technologies for the capture, utilization, and storage of carbon dioxide (CO2), we need fundamental knowledge and control of chemical interactions associated with the capture and conversion of the molecule into high-value chemicals, minerals, and all kinds of materials. Bulk magnesium oxide (MgO) is frequently used for the trapping and storage of CO2 by the generation of magnesium carbonates. In this study, the growth and reactivity of MgO nanostructures on a Cu2O/Cu(111) substrate were investigated by using scanning tunneling microscopy (STM) and synchrotron-based ambient-pressure X-ray photoelectron spectroscopy (AP-XPS). For extremely small concentrations of Mg (similar to 0.01 monolayer (ML)), a well-ordered film of copper oxide with small clusters (0.2-0.5 nm in width, 0.4-0.6 & Aring; in height) of embedded MgO was seen. At a coverage of 0.1 ML, MgO nanoparticles with a width of 0.4 to 1 nm and a height of similar to 1.5 & Aring; were randomly distributed on the copper oxide. Random distribution was also observed when the MgO coverage was raised to 0.25 ML, with the width of the MgO particles increasing to 2-2.5 nm and the height reaching 2 & Aring;. These oxide nanostructures displayed a high reactivity toward CO2 and H-2 that is not seen for bulk MgO. Dissociation of H-2 was observed at room temperature with the reaction of the H adatoms with CuOx and C-containing groups. On the small MgO nanostructures (<1 nm in width), instead of plain carbonate formation, there was dissociation of CO2 into CO and C species, opening reaction channels for the conversion of this harmful molecule into oxygenates and light alkanes.