| Abstract
| - A comparative study of carbon gasification with O2 and CO2 was conducted by using densityfunctional theory calculations. It was found that the activation energy and the number of activesites in carbon gasification reactions are significantly affected by both the capacity and mannerof gas chemisorption. O2 has a strong adsorption capacity and the dissociative chemisorption ofO2 is thermodynamically favorable on either bare carbon surface or even isolated edge sites. Asa result, a large number of semiquinone and o-quinone oxygen can be formed indicating asignificant increase in the number of active sites. Moreover, the weaker o-quinone C−C bondscan also drive the reaction forward at (ca. 30%) lower activation energy. Epoxy oxygen formsunder relatively high O2 pressure, and it can only increase the number of active sites, not furtherreduce the activation energy. CO2 has a lower adsorption capacity. Dissociative chemisorption ofCO2 can only occur on two consecutive edge sites and o-quinone oxygen formed from CO2chemisorption is negligible, let alone epoxy oxygen. Therefore, CO2−carbon reaction needs (ca30%) higher activation energy. Furthermore, the effective active sites are also reduced by themanner of CO2 chemisorption. A combination of the higher activation energy and the fewer activesites leads to the much lower reaction rate of CO2−carbon.
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