Unveiling the intrinsic “molecular engine” driven autocatalytic cycle in coal combustion: A combined experimental and DFT investigation

Efficient and clean coal utilization is a core component of the Dual-Carbon Strategy, dependent on innovation and deep mechanistic understanding. Current experimental studies often deviate significantly from industrial combustion conditions. In this study, an integrated preheating-instantaneous heating combustion simulator was employed to reproduce the realistic combustion state of pulverized coal under oxygen-enriched, high-velocity gas flow conditions. Combustion experiments were conducted under coupled preheating and rapid-heating conditions at different atomic oxygen-to-carbon ratios ( A O/C ). The results show that when A O/C = 2.0-3.8, the burnout ratio ( η ) of coal increases from 63% to 91% with increasing A O/C , revealing that the steady-state persistence of radical reactions contributes to the optimization of η . Furthermore, the combustion process is primarily governed by the synergistic evolution between oxygen-containing functional groups and aliphatic hydrocarbon structures within the disordered carbon phase on the particle surface. Density Functional Theory (DFT) calculations indicate that coal combustion proceeds via an autocatalytic cyclic system driven by an intrinsic “molecular engine” ROS·OH. The cleavage of peroxide radicals (R-O-O·) provides the energy drive for the generation of the system's “molecular engine”ROS·OH (Reactive Oxygen Species). This ROS·OH species exhibits extremely high reactivity, with a remarkably low reaction barrier ( E a = 6.22 kJ·mol −1 ) toward functional group activation, effectively inducing their transformation into highly reactive radicals Ar-R-O· and Ar-R·. The significant exothermicity of this process further promotes the β -scission of Ar-RO· to yield gaseous CO and CO 2 as well as Ar–R·, which subsequently reenters the initial reaction with O 2 . This chain-propagating mechanism establishes an autocatalytic radical cycling network, achieving efficient internal energy conversion and sustaining the overall combustion reaction.