Theoretical Insights into the Mechanism of CO₂ Chemisorption and Subsequent CO Desorption on Char Surface with Zigzag Active Sites

ABSTRACT

A detailed mechanism accounting for CO₂ 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 CO₂, 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, CO₂ 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-CO₂ 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.

KEYWORDS:

• Char
• CO₂
• Density functional theory (DFT)
• Mechanism
• Transition state theory (TST)

Funding

This work was supported by National Natural Science Foundation of China (91441129, 51210010, 51176118) and the National Basic Research Program of China (973 Program) (2013CB228502).

Additional information

Funding

This work was supported by National Natural Science Foundation of China (91441129, 51210010, 51176118) and the National Basic Research Program of China (973 Program) (2013CB228502).