Density Functional Theory Study On Oxidation Mechanism Of Coke With High Coverage Oxygen Adsorption

Coal has always been an important part of energy in our country and the world.In recent centuries,we have produced serious pollution and accumulation of greenhouse gases while mining and utilizing coal resources.In the future,carbon will reach its peak.Neutrality with carbon will be an important direction of energy development,and the clean and efficient use of carbon will be an essential part of it.Due to the complexity of the coal combustion process,including pyrolysis and heterogeneous reactions,the understanding of the coke oxidation mechanism is not comprehensive.The research on the relevant mechanism is beneficial to the more effective utilization of coal resources,and the requirements are urgent.In addition,the coke oxidation process under low temperature conditions is also very important,which has an important impact on the high-efficiency low-temperature combustion technology of coal,as well as coal storage and coking processes.In this paper,from the perspective of quantum chemistry,using Gaussian09 calculation software,the oxidation process of Zigzag oxygen adsorption coke model structure is calculated,and different reaction paths of related carbon oxides are obtained.The analysis of the reaction process is based on the transition state theory,and the DFT density functional method is selected for structural optimization and energy calculation.Taking the oxygen adsorption structure on the coke Zigzag surface as the starting point of the reaction,the first step of the reaction,that is,the breaking of the C-C bond of the outer carbon atoms,needs to overcome a high energy barrier.The first step of this part of the reaction is the fracture of C-C bond at the outermost carbon atom layer,which needs to overcome an energy barrier of 196.65/306.48 k J mol^-1.Then,after a series of intermediate reactions in the outermost layer and overcoming the corresponding lower energy barriers,a structure similar to carbonyl will form.Then,carbonyl can be directly desorbed to form the oxidation product CO,with the corresponding lower energy barrier of 8.28/48.37 k J mol^-1 respectively.For CO desorption,the desorption mode also contains the direct desorption from the initial structure.The energy barrier of this process is the highest,which is 562.96 k J mol^-1.Therefore,this part of the reaction may occur at very high temperature because it requires a lot of energy.The generation of CO₂ requires the migration of carbonyl groups in the outer oxygen atomic layer to form a relatively stable carbon-oxygen six-membered ring structure.There are three similar way to desorb CO₂:breaking two C-O bonds at the same time directly desorbs CO₂,breaking the C-O bond to form a chain structure and finally desorbing CO₂,or forming a CO2-char hetero-structure to complete CO₂ desorption in the form of breaking the C-C bond,respectively.In this paper,the research content covers the migration,rearrangement and desorption of oxides on the surface of coke model.It is found that there are two ways of CO desorption:direct and indirect desorption,while CO₂ cannot be desorbed directly,that is,it can only be desorbed after rearrangement to a certain structure.In the kinetic part,the thermodynamic and chemical kinetic results of different reaction paths are compared with the experimental results in the literature.The possible oxidation paths under the condition of high coverage oxygen adsorption are studied,and several typical desorption modes of oxidation products are obtained comprehensively,which provides potential theoretical guidance and reference for combustion control,industrial coal coking and coal utilization.