Modelling carbon chemisorption on a nickel catalyst. MINDOSR semiempirical calculations

Autor: Flor Marina Poveda, Anibal Sierraalta, Fernando Ruette, JoséL. Villaveces
Rok vydání: 1996
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Zdroj: Journal of Molecular Catalysis A: Chemical. 106:109-118
ISSN: 1381-1169
DOI: 10.1016/1381-1169(95)00246-4
Popis: Calculations for C chemisorption on a finely divided nickel catalyst modeled by Ni5, Ni7 and Ni14 clusters were carried out by using the MINDO SR semiempirical method. Vertical adsorption on several sites in the border and in the center of these clusters were evaluated. The adsorption energy depends not only on the type of site but also on the cluster size, due to large changes in the coordination of the atoms forming the adsorption site. Results obtained optimizing the adsorbate geometry on the surface clearly indicate that thermodynamically favored chemisorptions occur mainly on border sites. Sites formed of atoms equally coordinated show smaller differences in adsorption energies than those with different saturation. Relaxation of the cluster and high C coverage favored chemisorption on four-fold center sites and induced carbon penetration into the bulk. Chemisorption of carbon produces a decrease of the magnetic moment of the metal surface. The introduction of the diatomic binding energy (DBE) allows us to interpret adsorption processes in terms of the energetic changes of the involved bonds. Thus, some adsorption sites with small adsorption energy (AE) would be strongly active sites because of high DBE values. A model for carbon diffusion into the Ni bulk is presented.
Databáze: OpenAIRE
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