Effect of molecular structure evolution during low-temperature oxidation of bituminous coal on physisorption of oxygen

• The higher the oxidation degree of coal, the lower the physisorption amount of oxygen. • Nitrogen-containing aromatic rings exhibit the strongest adsorption capacity, followed by ether bonds, carbonyl group, and methylene, while alicyclic rings show the weakest adsorption capacity. • During low-temperature oxidation of coal, the reduction of aliphatic structures is the main factor in the decrease of the physisorption amount of oxygen. • Methylene and carbonyl groups are ideal targets for inhibiting coal spontaneous combustion due to their strong adsorption capacity as well as high abundance. Spontaneous combustion caused by low-temperature oxidation (LTO) of coal is a significant danger to mining safety, and physisorption of oxygen on coal is a crucial initial step in this oxidation process. This paper combines experiments with molecular simulations to study the mechanism by which the evolution of the molecular structure of bituminous coal during LTO influences the physisorption of oxygen. First, based on temperature programmed experiments, the LTO stages of coal were divided, and then carbon-13 nuclear magnetic resonance ( 13 C NMR) and X-ray photoelectron spectroscopy (XPS) characterization data were used to construct molecular models of coal in four different oxidation stages. Additionally, the physisorption behavior of oxygen on coal with different degrees of oxidation was studied using grand canonical monte carlo (GCMC) simulations. Finally, the radial distribution function (RDF) and molecular structure parameters were combined to investigate the influence of different molecular structures of coal on physisorption of oxygen. The results indicate that the physisorption amount of oxygen is negatively correlated with the degree of coal oxidation. Nitrogen-containing aromatic rings, such as pyrrole and pyridine, exhibit the strongest physisorption capacity, followed by ether bonds, carbonyl group, and methylene, while alicyclic rings show the weakest physisorption capacity. The reduction in methyl and methylene groups is the main reason for the decrease in physisorption amount, while the conversion of some aliphatic structures to carbonyl groups can partially offset the loss of physisorption amount. The results of this study provide a reference for the development of targeted inhibitors for coal spontaneous combustion.