Study on CO/CO₂ formation mechanism of Zigzag model coke with high oxygen coverage based on DFT theory

The clean and efficient utilization of carbon resources is becoming more and more important, in energy, material, and chemical engineering field, but the mechanism of coke oxidation, especially that of the CO₂/CO desorption is not fully studied yet. In this paper, density functional theory was used to study the oxidation mechanism of Zigzag char structure with high coverage of O₂, which is related to an oxidation under lower temperature or high pressure. Based on the corresponding quantum chemistry calculation, it is shown that there are several possible pathways for the CO₂ desorption process, which may need rearrange to form the structure containing O−C−O clusters. And successively, multiple intermediate reaction steps are required to complete the desorption of CO₂. Other than in the literature that the COO–O–C functional group formed first, with then the C–O bond broken and CO₂ desorbed respectively, a novel pathway with two C–O bonds broken simultaneously to generate CO₂ was found. It results from a functional group of COO–char formed, and certain alternative pathways via C–C bonds breaking were also dealt with, as well as related CO desorptions. The reaction model built was validated by theoretical and experimental results from literature satisfactorily.