Study On Coke Oxidation With Density Functional Theory

For a long time,coal has been a major component of the world,especially China’s energy,in the coming decades,but it has brought us both energy and resources,as well as serious pollution and greenhouse gases.Over the years,due to its complexity,people have not clearly understood the mechanism of oxidation of carbon,which makes it difficult to use it fully and effectively.In this paper,the quantum chemical calculation simulation software Gaussian09 is used to investigate the mechanism of the reaction between coke and oxygen in two possible structures of zigzag and armchair.DFT/B3LYP,DFT/B3PW91 and MP2 were used to calculate respectively.DFT/B3LYP was selected as the calculation method by contrast analysis.The selected base set is 6-31G（d）,and its structure is geometrically optimized.B3LYP/6-311++G（d,p）is used for single point energy calculation,and zero point can be used for calculation of structural energy.Based on this calculation,the system was analyzed for spin multiplicity and active sites.When O₂ is chemisorbed on the surface of the ziazag structure,it has no barrier reaction and a large amount of exotherm.The exotherm is 758.40 kJ/mol.The direct desorption of CO needs to overcome the energy barrier of 347.22 kJ/mol.It can be seen that the heat released by chemical adsorption is sufficient for direct CO desorption.The second desorption process is accompanied by the occurrence of a concentrated reaction,forming a stable intermediate structure,and a second desorption process can occur,which requires an energy barrier of 293.49 kJ/mol.At the same time,it can also form the adsorption structure of CO₂,only need to overcome the energy barrier of 14.16 kJ/mol,and finally desorb CO₂.When oxygen is chemisorbed on the coke surface of the armchair structure,the energy barrier that needs to be overcome in each intermediate reaction is small,and the heat released is much,and the heat released during the whole reaction process is 573.20 kJ/mol.Subsequently,the desorption process of two CO molecules occurred continuously.The energy barrier to be overcome in the first CO desorption was 283.45 kJ/mol;and the energy barrier to be overcome in the second CO desorption was 423.93 kJ/mol.Since the second CO desorption requires a large amount of energy,the reaction must occur at high temperatures.In this study,a coke surface oxide model with a carbonyl functional group was used as a research object to study the desorption,migration,and rearrangement processes of coke surface oxides.The results show that the CO produced by the armchair model of the armchair structure and O₂ cannot be directly desorbed,and it must be rearranged before desorption.By comparison,it was found that the rearrangement and migration reactions occurred faster on the surface of the zigzag and armchair structures than the desorption reaction.The thermodynamic and chemical kinetic calculations of the established model are compared with the experimental results of the literature,and the rationality is verified.For the first time,the study reveals the reaction path of coke oxidation process,which will provide theoretical guidance and reference for the regulation and utilization of the corresponding combustion process.