The effect of different In2_2O3_3(111) surface terminations on CO2_2 adsorption

In$_2$O$_3$-based catalysts have shown high activity and selectivity for CO$_2$ hydrogenation to methanol, however the origin of the high performance of In$_2$O$_3$ is still unclear. To elucidate the initial steps of CO$_2$ hydrogenation over In$_2$O$_3$, we have combined X-ray Photoelectron Spectroscopy (XPS) and Density Functional Theory (DFT) calculations to study the adsorption of CO$_2$ on the In$_2$O$_3$(111) crystalline surface with different terminations, namely the stoichiometric, the reduced, and the hydroxylated surface, respectively. The combined approach confirms that the reduction of the surface results in the formation of In ad-atoms and that water dissociates on the surface at room temperature. A comparison of the experimental spectra and the computed core-level-shifts (using methanol and formic acid as benchmark molecules) suggests that CO$_2$ adsorbs as a carbonate on all surface terminations. We find that CO$_2$ adsorption is hindered by hydroxyl groups on the hydroxylated surface.Comment: 49 pages, 18 figure

Tetrahelix conformations and transformation pathways in Pt1Pd12 clusters

The threshold method is used to explore the potential energy surface of the Pt1Pd12 bimetallic cluster, defined by the Gupta semiempirical potential. A set of helical structures, which follow a Bernal tetrahelix pattern, correspond to local minima for the Pt1Pd12 cluster, characterizing the region of the energy landscape where these structures are present. Both right-handed and left-handed chiral forms were discovered in our searches. Energetic and structural details of each of the tetrahelices are reported as well as the corresponding transition probabilities between these structures and with respect to the icosahedron-shaped global minimum structure via a disconnectivity graph analysis

Initial oxidation of Cu(100) studied by X-ray photo-electron spectroscopy and density functional theory calculations

Density functional theory calculations and ambient pressure X-ray photoelectron spectroscopy are used to investigate initial oxidation of Cu(100). Surface stability with respect to oxygen coverage is calculated together with O 1s core level shifts. Oxidation of Cu(100) is found to occur via the formation of a p(2 × 2) overlayer (0.25 ML) followed by a reconstructed (22 × 2)R45° -O missing-row (MR) structure (0.50 ML). A c(4 × 6) structure with a 0.3 ML coverage is close in stability for intermediate oxygen chemical potentials. The relative stability is found to be weakly dependent on the applied exchange-correlation functional. The calculated shifts in the O 1s binding energy are in good agreement with the measured evolution of the binding energy. The shift to higher O 1s binding energies with increasing oxygen coverage is found to correlate with the charge on neighboring copper atoms. The O 1s core-level shifts here obtained with CO2 as oxidant, are similar to previous measurements of Cu(100) oxidation with O2