Abstract
A detailed mechanism accounting for CO
2
chemisorption and subsequently CO desorption on char surface with zigzag active sites has been investigated using accurate ab initio density functional theory B3LYP/6-311+G(d,p) calculations. The HOMO-LUMO gaps indicate that char donates electrons to CO
2
, which is tempted by small electron confinement capability of the surface active C atom. In single-site adsorption, the carbonyl-type oxygen groups can be formed, whereas the heterocyclic oxygen and the lactone groups can be formed via dual-site adsorption. It was found that the former process is endothermic and the latter process is exothermic. In this study, CO
2
chemisorption products can be influenced by the electronic environment in terms of the optimized bond length. The reaction channels accounted for CO desorption from char-CO
2
complex and the evolution from lactone group to a cyclic ether structure were determined. The rate coefficients were evaluated by transition state theory theory in the temperature range of 300-2500 K. The results showed that the CO desorption reaction is competitive, and the evolution from lactone group to a cyclic ether structure is kinetically supported. In addition, the carbonyl-type oxygen groups are more likely converted from heterocyclic oxygen groups instead of direct single-site adsorption.