Effect of surface site on the spin state for the interaction of NO with Pd2, Rh2 and PdRh nanoparticles supported at regular and defective MgO (001) surfaces

Author(s): S.AbdelAal

An attempt has beenmade to analyze the effect of surface site on the spin state for the interaction ofNOwith 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 transitionmetal dimers, PdRh, that deposited onMgO(001) surface have been studied bymeans of hybrid density functional theorycalculations and embedded clustermodel. The most stable NO chemisorption geometry is in a bridge position on Pd2 and a top configuration of Rh2 and PdRhwithN-down oriented.NOprefers binding to Rh sitewhen both Rh and Pd atoms co-exist in the PdRh. The natural bond orbital analysis (NBO) reveals that the electronic structure of the adsorbedmetal represents a qualitative changewith respect to that of the freemetal. The adsorption properties ofNOhave been analyzedwith reference to theNBO, charge transfer, band gaps, pairwise and non-pairwise additivity. ThebindingofNOprecursor isdominatedbythe 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 themetal–metal interaction due to the relatively strong bondwith the substrate. Spin polarized calculationswere performed and the results concernthe systems intheirmorestable spinstates. Spin quenchingoccurs forRh 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 highspin states.Themetal–support and dimer–support interactions stabilize the low spin states of the adsorbedmetalswith respect to the isolatedmetals and dimers.Although the interaction of Pd, Rh, Pd2, Rh2 and PdRh particleswith Fs sites ismuch stronger than the regular sites O2-, the adsorption ofNOis stronger when the particular dimers are supported on an anionic site than on an Fs site of theMgO(001). The encountered variations inmagnetic properties of the adsorbed species atMgO(001) surface are correlatedwith the energy gaps of the frontier orbitals. The results show that the spin state of adsorbedmetal atoms on oxide supports and the role of precursor molecules on the magnetic and binding properties of complexes need to be explicitlytaken into account.

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