Alloying Effects on N−O Stretching Frequency:  A Density Functional Theory Study of the Adsorption of NO on Pd₃Mn (100) and (111) Surfaces

Abstract

We present total energy and N−O stretching frequency calculations for the low-coverage adsorption of NO on palladium−manganese Pd3Mn (100) and (111) surfaces, on the basis of density-functional theory periodic calculations. A complete description of all the different adsorption sites and corresponding N−O vibrations is given and a theoretical interpretation of the experimental IR spectra is proposed. On both Pd3Mn (100) and (111) surfaces, the highly coordinated vertical adsorption sites are always energetically favored. The atop adsorption on the surface manganese atom is also a stable site. On Pd3Mn (100), a new horizontal dibridge site is reported. The adsorption on these palladium−manganese alloy surfaces is weaker than the adsorption on the pure corresponding palladium surfaces. The anharmonic N−O stretching frequencies on the Pd3Mn surfaces are shifted by 60−100 cm-1 toward the lower frequencies by comparison with the pure palladium surfaces. The weakening of the adsorption strength and the global shift for the N−O frequencies has been correlated with the presence of the surface manganese atoms, which play a predominant role for the electronic interactions between the magnetic NO molecule and the alloy periodic surface. An interpretation of the alloying effect on the strength of the N−O bond and the NO adsorption is proposed on the basis of a qualitative Mulliken population analysis. The empty states on the surface manganese atoms are responsible for an increased electron-transfer toward NO, and hence of the smaller vibrational frequency on the alloy compared to pure Pd. Indeed these empty states interact with the π*NO and push it below the Fermi level, resulting in a transfer from the “surface electron reservoir” toward the π*NO molecular orbital.

CH3O Decomposition on PdZn(111), Pd(111), and Cu(111). A Theoretical Study

“…56 DF slab model results provided evidence that fcc and hcp sites exhibit basically the same adsorption propensity for CO, with essentially equal binding energies of 194 kJ mol -1 (fcc) and 191 kJ mol -1 (hcp) at 1/3 coverage. 57 Our calculated binding energies, 179 kJ mol -1 (fcc) and 177 kJ mol -1 (hcp), also support this conclusion. The binding energy on top of Pd atoms is calculated to be almost 60 kJ mol -1 smaller than at hollow sites; this is comparable to the energy difference calculated for H adsorbed at hollow and top sites of Pd(111) (Table 2).…”

Density functional theory study of the adsorption and reaction of C2H4 on Fe3C(100)

“…In configurations a1, a2, and a3, C2H4 adsorbs on the exposed first Fe layers by π coordination. The C and H atoms of C2H4 are in approximately the same plane, while both the two C atoms bond with the same Fe atom in the substrate to form a σ-π compound with a three-membered C-Fe-C ring structure [35]. The adsorption energies of three configurations are 0.39, 0.52, and 0.53 eV.…”

Theoretical Study of CO and NO Chemisorption on RhCu(111) Surfaces

“…The present settings are similar to those used in previous studies. 31,33,53,54 In the present periodic models of the (111) surface of mono and bimetallic systems a (4 × 4) supercell has been chosen, each atomic layer contains 16 metal atoms and, hence, the unit cell used in the calculations involves a total of 80 metal atoms. This large supercell guarantees that in the RhCu models there are always metal surface atoms with the coordination corresponding to the bulk metal.…”