Atomistic processes of Ni and Pd atoms on MgO(001) surfaces with surface-functional hydroxyl groups: Ab-initio calculations

By using ab-initio calculations based on the density functional theory, we systematically studied the adsorption and the diffusion properties of Ni and Pd (X_M) atoms on hydroxylated MgO(001) [MgO_hdr(001)] surfaces. The energetics of adsorption, binding, and diffusion are presented and compared with those of X_M atoms on clean MgO(001). The calculated energetics showed considerably enhanced adsorption of X_M on MgO_hdr(001) compared to that on MgO(001). The stronger binding of X_M and OH on MgO(001) indicated the favorable formation of X_MOH complexes instead of X_M dimers on the surface. In the case of surface diffusion, X_MOH on MgO(001) was observed to diffuse via a hopping process over the surface hollow sites. The diffusion of X_MOH on MgO(001) was slightly faster than that of X_M atoms. Compared to the surface diffusion of PtOH on MgO(001), the surface diffusion energy barriers were in the following order, PtOH (0.89 eV) > NiOH (0.71 eV) > PdOH (0.43 eV). Therefore, the surface dynamics of Ni, Pd, and Pt on MgO_hdr(001) driven thermally at temperatures relevant to the catalytic activities of metal clusters are expected to be different. The electronic structures and the charge states of X_MOH on MgO(001) were analyzed further and compared with those of X_M on MgO(001).