ABSTRACT It is imperative to have an in-depth understanding of the pathway and mechanism of coal-oxygen-water coupling reaction during low-temperature oxidation of coal, not only for preventing fires in the coal industry but also for reducing emissions of hazardous gases. In this study, in-situ Infrared spectroscopy characterization and quantum chemical calculations were combined to investigate in detail the chemical interactions between coal, moisture, and oxygen. In-situ infrared oxidation experiments ascertained the types and amounts of hydroxyl, aliphatic hydrocarbon, and carbonyl functional groups in lignite coal samples with varied moisture content during LTO. Subsequently, three typical molecular structures of functional groups mainly involved in the coal-oxygen reaction were chosen as the research representatives, and their reactivity was analyzed using density functional theory (DFT). Thus, the main reaction pathways of these functional groups during the LTO of coal were studied using quantum chemical methods. The results indicated that the moisture in coal significantly affected the coal–oxygen reaction by altering the chemisorption processes in the coal–oxygen combination and the active sites in coal molecules. Quantitative calculation of thermodynamic parameters such as the enthalpy and activation energy showed that moisture had a promoting effect on some reaction steps while hindering others. Moreover, the mechanism of coal-oxygen-water coupling reaction was also explored based on the reaction sequence of intermediate complexes.
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