Transition-metal atom adsorption on an ${\mathrm{F}}_s$ defect site of MgO (100) and the interaction with a hydrogen atom

The interaction of transition metals belonging to the group Pt-Pd-Ni and the period Ni-Cu-Zn, with an ${\mathrm{F}}_s$ center of the MgO (100) surface was investigated using density functional theory. This study was aimed at finding the effect of the electron delocalization of an MgO oxygen vacancy on the interaction energies of the metals with the defect and the electronic configuration of the adsorbed metal atom. The degree of electron delocalization was determined from the maximum values of the electron localization function (ELF). It is confirmed that there are two electrons largely localized in the center of the ${\mathrm{F}}_s$ vacancy. These electrons can delocalize over an adsorbed metal atom. This is the reason for the stabilization of some surface complexes. The MO analysis shows that the filling and the symmetry of the last occupied orbitals of the complex $\mathrm{M}\text{−}{\mathrm{F}}_s∕\mathrm{Mg}\mathrm{O}$ depends on the kind of metal. In the case of Ni and Pt the orbitals from HOMO until HOMO-4 are d orbitals and the interaction orbital is the HOMO-5, while for Pd the interaction orbital is the HOMO and the orbitals HOMO-1 until HOMO-5 are d character. This information is very useful for the study of the interaction of a hydrogen atom with del metal-${\mathrm{F}}_s∕\mathrm{Mg}\mathrm{O}$ complex. The oxygen vacancy modifies the interaction of a hydrogen atom with a metal deposited on the defect site due to changes in the electronic configuration of the metal. Therefore, the chemical activity of the metal strongly depends on the interaction metal support.

Figure 1

Schematic representation view of the localization domains of the electron localization function for the ground state of the oxygen vacancy at an isosurface value of $\eta =0.70$. The electrons of the vacancy are higly located and have a domain that expands beyond the surface of the cluster.

Figure 2

Comparison of the binding energies and maximum value for the $\mathrm{ELF}\left(\eta \right)$ of the defect’s basin along (a) group and (b) period.

Figure 3

Schematic representation view of the localization domains of the electron localization function for the ground state of the $\mathrm{M}∕{\mathrm{F}}_s$ complexes. (a) $\mathrm{Pt}∕{\mathrm{F}}_s$ complex at an isosurface value of $\eta =0.30$. (b) $\mathrm{Pd}∕{\mathrm{F}}_s$ complex at an isosurface value of $\eta =0.30$. (c) $\mathrm{Ni}∕{\mathrm{F}}_s$ complex at an isosurface value of $\eta =0.30$.

Figure 4

Schematic representation view of the localization domains of the electron localization function for the ground state of the $\mathrm{M}∕{\mathrm{F}}_s$ complexes. (a) $\mathrm{Cu}∕{\mathrm{F}}_s$ complex at an isosurface value of $\eta =0.30$. (b) $\mathrm{Zn}∕{\mathrm{F}}_s$ complex at an isosurface value of $\eta =0.30$.