Opposite roles of O-2 in NO- and N2O-carbon reactions: An ab initio study

Citation
Zh. Zhu et al., Opposite roles of O-2 in NO- and N2O-carbon reactions: An ab initio study, J PHYS CH B, 105(4), 2001, pp. 821-830
Citations number
36
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Physical Chemistry/Chemical Physics
Journal title
JOURNAL OF PHYSICAL CHEMISTRY B
ISSN journal
1520-6106 → ACNP
Volume
105
Issue
4
Year of publication
2001
Pages
821 - 830
Database
ISI
SICI code
1520-6106(20010201)105:4<821:OROOIN>2.0.ZU;2-U
Abstract
Previous experimental studies showed that the presence of O-2 greatly enhan ces NO-carbon reaction while it depresses N2O-carbon reaction on carbon sur faces. A popular explanation for the rate increase is that the addition of O-2 results in a large number of reactive carbon-oxygen complexes, and deco mposition of these complexes produces many more active sites. The explanati on for the latter is that excess O-2 simply blocks the active sites, thus r educing the rate of N2O-carbon reaction. The contradiction is that O-2 can also occupy active sites in NO-carbon reaction and produce active sites in N2O-carbon reduction. By using ab initio calculation, we find that the oppo site roles of O-2 are caused by the different manners of N2O and NO adsorpt ion on the carbon surface. In the presence of excess O-2, most Of the activ e sites are occupied by oxygen groups. In the competition for the remaining active sites, NO is more likely to chemisorb in the form of NO2 and NO che misorption is mon thermodynamically favorable than O-2 chemisorption. By co ntrast, the presence of excess O-2 makes N2O chemisorption much less therma lly stable either on the consecutive edge sites or edge sites isolated by s emiquinone oxygen. A detailed analysis and discussion of the reaction mecha nism of N-2 formation from NO- and N2O-carbon reaction in the presence of O -2 is presented in this paper.