Adsorption of NO on Pd and Pd2 supported at the regular and defective CdO (0 0 1) surfaces: Density functional theory study

The adsorption of NO on Pd atoms and homonuclear transition metal dimers, Pd2, deposited on O2− and Fs sites of the CdO (0 0 1) surface was studied by density functional calculations and an embedded cluster model. Geometrical optimization of adsorption of the molecule NO on Pd/CdO and Pd2/CdO with different spin states at particular sites was conducted. Spin polarized calculations were performed, and the systems in the most stable spin states were determined. Spin quenching occurs for Pd2 complexes at the terrace and defective surfaces. Supported Pd2 stabilized the low spin states of the adsorbed metals in comparison with free Pd2. Although the interaction of Pd and Pd2 particles with Fs sites is much stronger than with regular O2− sites, the adsorption of NO is stronger on Pd2/CdO (O2−) than on Pd2/CdO (Fs) with low spin state. Nevertheless, the greater interaction of NOPd and NOPd2 at O2− sites increases the energy required to switch from high to low spin. The variations observed in the magnetic properties of the adsorbed species at the CdO (0 0 1) surface are correlated with the energy gaps of the frontier orbitals. The adsorption properties of NO were analyzed with reference to the natural bond orbital, charge transfer, band gaps, the total charge-density contours, and pairwise and non-pairwise additivity. The binding of NO precursor is dominated by the E(i)Pdx−NO pairwise additive components, and the role of the support was not restricted to the metal or the dimer.