A. Montoya et al., CO desorption from oxygen species on carbonaceous surface: 1. Effects of the local structure of the active site and the surface coverage, J PHYS CH A, 105(27), 2001, pp. 6757-6764
A systematic theoretical study using the density functional theory is perfo
rmed to provide molecular-level understanding on the desorption of carbon m
onoxide from surface oxygen complexes that are formed in the gasification a
nd combustion of coal. Particularly, a CO molecule release from carbonyl ox
ygen complexes in the presence of different oxygen environments was analyze
d. Molecular carbonyl models of different sizes in the zigzag, armchair, an
d tip shapes of the active sites were selected. It was found that the shape
of the local active site has a strong effect on the CO desorption energy,
and they are correlated with the broaden feature of the CO molecule desorpt
ion in the temperature-programmed desorption (TPD) experiments of oxidized
carbonaceous material. The calculated desorption activation energy range is
in good agreement with experimental data. Molecular size convergence analy
ses on the carbonyl models suggest that the smallest graphene molecular sys
tem for accurate desorption structure on char is a three-ring molecule. The
activation energy and normal-mode analyses for selected carbonyl complexes
suggest that carbonyl surface oxygen complexes are stable structures and t
hat they can be considered as labile surface oxygen complexes. The CO molec
ule desorption energy is affected by the influence of different neighboring
surface oxygen groups on the carbon surface as well as the aromatic charac
ter of the molecular models. The desorption energy analysis suggests that t
he CO molecule can be adsorbed on clean carbonized surface to form stable s
tructures. The preadsorbed oxygen group decreases the CO adsorption stickin
g probability on oxidized materials, but it remains an energetically favora
ble process.