Figure 1

Surface phase diagram for the (111) facet under constrained thermodynamic equilibrium with oxygen and ethylene. Solid (dot-dashed) lines represent the stability limit with respect to the formation of ${\mathrm{CH}}_3\mathrm{CHO}$ (${\mathrm{C}}_2{\mathrm{H}}_4\mathrm{O}$). Each shaded area represents the region of stability of a combination of two surface structures giving a Cu coverage of 0.5 ML. The white area is the region of stability of the clean Ag(111) surface. The dashed polygon corresponds to typical values of temperature and pressures used in experiments ($T=300–600\mathrm{K}$ and $p_{{\mathrm{O}}_2}$, $p_{{\mathrm{C}}_2{\mathrm{H}}_4}={10}^{-4}-1\mathrm{atm}$). ${\mathrm{Ag}}_{1.2}\mathrm{O}$ and ${\mathrm{Ag}}_{1.5}\mathrm{O}$ are 1-layer thin oxidelike structures; CuO and CuO(b) are 1-layer thin and bulk CuO structures, respectively; $p2$ and $p4\mathrm{\text{−}}{\mathrm{OCu}}_3$ are 1-layer thin ${\mathrm{Cu}}_2\mathrm{O}$-like structures with ($2\times 2$) and ($4\times 4$) periodicity, respectively. In the latter, a ${\mathrm{OCu}}_3$ unit is removed.Reuse & Permissions

Figure 2

Top: relaxed geometries of four of the most stable oxidelike structures. Large (gray) spheres represent Ag atoms, small (red) spheres O atoms and dark (blue) spheres Cu atoms. Bottom: Surface energy of the most stable surface structures on each of the three surface orientations as a function of the Cu chemical potential. At selected Cu chemical potentials, also a model of a catalyst particle obtained through the Wulff construction is presented. $\Delta {\mu }_{\mathrm{O}}$ is set to $-0.61\mathrm{eV}$ (corresponding to $T=600\mathrm{K}$ and $p_{{\mathrm{O}}_2}=1\mathrm{atm}$).Reuse & Permissions

Figure 3

(a) The Cu $2p_{3/2}$ core level spectra of the Ag-Cu catalyst recorded under oxygen and reaction (${\mathrm{C}}_2{\mathrm{H}}_4:{\mathrm{O}}_2$) atmospheres (total pressure 0.5 mbar at 520 K). (b) Valence band spectra of the Ag-Cu catalyst under oxygen and reaction atmospheres (left). The valence band region close to the Fermi edge obtained from the difference spectra between Ag-Cu and pure Ag samples (right). At the bottom, valence band spectra of reference oxides are given.Reuse & Permissions