Effect of the Molecular Structure of Antioxidant Inhibitor on Coal Spontaneous Combustion and Inhibition Mechanisms

Coal spontaneous combustion generates large amounts of toxic and hazardous gases, posing serious risks to environmental safety and human health. Developing efficient inhibitors to suppress this process is, therefore, crucial for the safe and sustainable utilization of coal resources. In this study, ferulic acid and vanillin were selected to investigate how molecular structural differences influence inhibition performance. Programmed temperature rise experiments, thermogravimetric–differential scanning calorimetry, Fourier transform infrared spectroscopy, and quantum chemical calculations were employed to evaluate the inhibitory behavior and underlying mechanisms. The influence of molecular structural differences on inhibition performance was comparatively analyzed. The results showed a significant synergistic effect between ferulic acid and vanillin, with the composite system achieving a CO inhibition rate of 71.9% at 170 °C. In addition, inhibitor addition significantly delayed the characteristic oxidation temperatures of coal. The 2:1 composite exhibited the strongest inhibition effect, increasing the critical and ignition temperatures by 14.1 and 9.7 °C, respectively, while reducing the exothermic peak intensity by 1.5 mW/mg. Quantum chemical analysis indicated that both inhibitors suppress coal oxidation by scavenging active radicals through hydrogen atom transfer. The conjugated carboxyl structure of ferulic acid enhances hydrogen-donating ability and transition-state stabilization, whereas the aldehyde group in vanillin contributes to stronger inhibition during the early oxidation stage. This study provides experimental evidence and theoretical insight for the molecular design of efficient coal spontaneous combustion inhibitors.