| Abstract
| - A density functional theory study was carried out to evaluate different possibilities of heterogeneous CO2desorption in combustion/gasification reactions. First, we investigated the heterogeneous CO2 evolution inducedas a secondary reaction caused by the CO readsorption on an oxidized surface, which produces a carbonate-like surface complex. This functional group was found to decompose as CO2 with an activation energy of 60kcal/mol. Another possibility for heterogeneous CO2 formation during char combustion or gasification isthrough the molecular O2 chemisorption on a carbon active site of an oxidized graphene layer. The peroxycomplex thus formed undergoes rearrangement into a dioxiranyl complex, C(2O). This complex can evolveas CO2 with an activation energy of 48 kcal/mol. The CO2 desorption is facilitated by the presence of anepoxy complex near the edge of the graphene layer. The epoxy complex undergoes transformation into acyclic ether complex during the dioxiranyl decomposition. Transition states and energetic profiles of thesedecomposition reactions were determined. Variations of selected C−C, O−O, and C−O bonds were analyzedthrough the change in the bond orders calculated by natural bond orbital analysis. Overall, carbon oxidationreactions in the presence of epoxy functionalities are very important in the formation of heterogeneous CO2and of cyclic ether complexes.
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