An attempt has been made to analyze the effect of surface site on the spin state for the interaction
of NO with Pd2, Rh2 and PdRh nanoparticles that supported at regular and defective MgO(001)
surfaces. The adsorption properties of NO on homonuclear, Pd2, Rh2, and heteronuclear transition
metal dimers, PdRh, that deposited on MgO(001) surface have been studied by means of hybrid
density functional theory calculations and embedded cluster model. The most stable NO chemisorption
geometry is in a bridge position on Pd2 and a top configuration of Rh2 and PdRh with
N-down oriented. NO prefers binding to Rh site when both Rh and Pd atoms co-exist in the PdRh.
The natural bond orbital analysis (NBO) reveals that the electronic structure of the adsorbed metal
represents a qualitative change with respect to that of the free metal. The adsorption properties
of NO have been analyzed with reference to the NBO, charge transfer, band gaps, pairwise and nonpairwise
additivity. The binding of NO precursor is dominated by the ( )
Mx NO
i E − pairwise additive
components and the role of the support was not restricted to supporting the metal. The adsorbed
dimers on the MgO surface lose most of the metal-metal interaction due to the relatively strong
bond with the substrate. Spin polarized calculations were performed and the results concern the
systems in their more stable spin states. Spin quenching occurs for Rh atom, Pd2, Rh2 and PdRh
complexes at the terrace and defective surfaces. The adsorption energies of the low spin states of
spin quenched complexes are always greater than those of the high spin states. The metal-support
and dimer-support interactions stabilize the low spin states of the adsorbed metals with respect to
the isolated metals and dimers. Although the interaction of Pd, Rh, Pd2, Rh2 and PdRh particles
with Fs sites is much stronger than the regular sites O2−, the adsorption of NO is stronger when the
particular dimers are supported on an anionic site than on an Fs site of the MgO(001). The encountered
variations in magnetic properties of the adsorbed species at MgO(001) surface are
S. A. Aal
2
correlated with the energy gaps of the frontier orbitals. The results show that the spin state of adsorbed
metal atoms on oxide supports and the role of precursor molecules on the magnetic and
binding properties of complexes need to be explicitly taken into account. |
