Microstructural evolution and oxidation behavior of lignite pretreated in methane-bearing oxygen-deficient atmospheres

Relationships among atmosphere-induced pore accessibility, functional-group distribution, and subsequent thermal oxidation remain insufficiently resolved. Lignite from the Xiashijie Coal Mine was exposed at 30 °C for 2 h to six controlled gas compositions and subsequently characterized by low-temperature N 2 adsorption, FTIR, and TG-DSC during heating in air. Relative to the air-like reference RC-0, the CH 4 -free 18 % O 2 condition, RC-1, showed a lower measured BET surface area but higher total pore volume and average pore diameter. Within the fixed-18 % O 2 series, CH 4 addition produced modest measured pore-parameter differences, whereas decreasing O 2 at fixed 3 % CH 4 was associated with non-monotonic pore responses. RC-3, pretreated in 3 % CH 4 /18 % O 2 , showed the highest measured T 1 , T 3 , and T 4 values, while the maximum Stage IV1 and Stage IV2 reaction rates occurred in RC-2 and RC-5, respectively. FTIR revealed atmosphere-dependent differences in relative fitted band areas without the appearance of new dominant functional-group types. Collectively, the results support a qualitative, stage-dependent, and non-monotonic association among pretreatment composition, retained N 2 -accessible pore and relative spectral states, and subsequent oxidation in air.