Artículo
CO interaction with Au atoms adsorbed on terrace, edge and corner sites of the MgO(1 0 0) surface. Electronic structure and vibrational analysis from DFT
Fecha de publicación:
01/05/2009
Editorial:
Elsevier Science
Revista:
Surface Science
ISSN:
0039-6028
Idioma:
Inglés
Tipo de recurso:
Artículo publicado
Clasificación temática:
Resumen
The interaction of CO with Au atoms adsorbed on terrace and low-coordinates sites (edge and corner) of the MgO(1 0 0) surface was studied using the density functional theory (DFT) in combination with embedded cluster models. Surface anionic (O2-) and neutral oxygen vacancy (Fs) sites were considered. In all the cases, the CO stretching frequencies are shifted with respect to free CO with values between -232 and -358 cm-1. In particular, the values for Au on Fs at edge and corner are shifted to higher stretching frequencies by 100 and 59 cm-1, respectively, with respect to the value on a perfect MgO(1 0 0) surface. This result is in agreement with recent scanning tunneling microscopy and infrared spectroscopy experiments where a corresponding shift of 70 cm-1 was observed by comparing the measurements on perfect and O-deficient MgO(1 0 0) surfaces. However, these results are different than expected because Au atoms on Fs centers are negatively charged and, therefore, according to the generally accepted scheme the CO frequency should be red-shifted with respect to the adsorption on anionic five-coordinated site where the Au atom is essentially neutral. The following picture emerges from the present results: the single occupied HOMO(α) of Au atom on Fs at low-coordinated sites consists in two lobes extended sideward the Au atom. For symmetry reasons, this MO overlaps efficiently with the 2π* MO of CO. This bonding contribution to the Au-CO link is counteracted by a Pauli repulsion between the 5σ MO of CO and more internal orbitals (the HOMO-1(α) and the HOMO(β)) centered on Au. In consequence, CO is forced to vibrate against a region with a high electron density. This is the so-called "wall effect" which by itself contributes to higher CO frequency values. © 2009 Elsevier B.V. All rights reserved.
Palabras clave:
Au/Mgo
,
Cluster Model
,
Co Adsorption
,
Dft
,
Model Catalysts
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Colecciones
Articulos(INQUISUR)
Articulos de INST.DE QUIMICA DEL SUR
Articulos de INST.DE QUIMICA DEL SUR
Citación
Ferullo, Ricardo; Fuente, Silvia Andrea; Belelli, Patricia Gabriela; Castellani, Norberto Jorge; CO interaction with Au atoms adsorbed on terrace, edge and corner sites of the MgO(1 0 0) surface. Electronic structure and vibrational analysis from DFT; Elsevier Science; Surface Science; 603; 9; 1-5-2009; 1262-1269
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