[Objective

]

In actual coal-hydrogen co-firing processes

the rapid combustion of hydrogen forms a localized hydrogen-rich atmosphere around char particles

and the intrinsic mechanism by which this pre-adsorbed hydrogen affects char-nitrogen oxidation remains largely unexplored. This paper aims to thoroughly investigate the microscopic oxidation mechanism of nitrogen-containing coke and the conversion pathways of nitrogen oxides(NO

x

) within the complex microenvironment of hydrogen-blended pulverized coal combustion

and facilitate the clean

efficient

and low-carbon utilization of coal resources. [Methods

]

Density functional theory(DFT) calculat

ions were rigorously conducted using the M06-2X exchange-correlation functional coupled with a 6-311G(d) basis set

a method that has been proven highly reliable for thermochemical kinetics of main-group elements. A zigzag edge model comprising seven carbon rings with a substituted pyridine nitrogen was established to effectively represent the typical local edge structures of pure coal char

alongside a correspondingly constructed pre-hydrogenated char model. Linear synchronous transit(LST) combined with quadratic synchronous transit(QST) methods were applied for locating transition states

validated by intrinsic reaction coordinate(IRC) and vibrational frequency analyses. Electrostatic potential(ESP) analysis was performed to visually evaluate and predict the initial adsorption behavior and preferential reactive sites of oxygen molecules. Subsequently

three representative competitive oxidation pathways resulting in different gas-phase products were systematically evaluated

identifying the respective transition states

intermediate complexes

and intrinsic reaction energy barriers to assess both kinetic and thermodynamic feasibilities. [Results

]

ESP visualizations reveal that the pre-hydrogenated coke model exhibits highly polarized surface features due to the uneven charge distribution caused by the synergistic effect of hydrogenation and nitrogen doping. The pre-adsorbed hydrogen atoms act as distinct electrophilic targets with significant positive charges

while the pyridine nitrogen atom serves as an electron-rich nucleophilic center. Reaction coordinate analysis demonstrates that the initial cleavage energy barrier of N—C bonds in the pure char skeleton is 237.4 kJ/mol. In contrast

this critical rate-determining step(RDS) barrier increases to 274.63 kJ/mol in the pre-hydrogenated char model

proving that surface hydrogenation substantially increases the ring-opening kinetic resistance of nitrogen-containing heterocycles. A comprehensive comparison among the three oxidation pathways on the pre-hydrogenated

char highlights striking differences. Pathway three

which leads to NO

2

formation

requires overcoming an exceptionally high energy barrier of 334.19 kJ/mol during the adsorption of the second O

2

molecule

rendering it kinetically unfavorable and negligible. Conversely

pathway one(producing NO and H_2O) and pathway two(producing NO and CO) emerge as the primary feasible competing routes. Both pathways share an identical kinetic bottleneck: the cleavage of the N—C bond within the nitrogen-containing heterocycle

which requires 274.63 kJ/mol. Thermodynamically

pathway one presents an overwhelming advantage

releasing a total energy of 692.76 kJ/mol compared to the 453.86 kJ/mol released by pathway two. However

once the shared RDS is overcome

pathway two exhibits a slight kinetic superiority during the desorption phases. [Conclusion

]

The oxidation of char in a hydrogen-doped microenvironment is fundamentally a high-temperature process rigidly controlled by the initial N—C bond cleavage. NO is conclusively the dominant nitrogen oxide product

whereas NO

2

formation is negligible under these constraints. By shedding light on the molecular-level pathways

this theoretical study bridges the gap between microscopic kinetics and macroscopic observations. The meticulously extracted intrinsic kinetic parameters offer reliable foundational data necessary to refine computational fluid dynamics(CFD) models for large-scale coal-hydrogen co-firing

ultimately aiding in the precise control and mitigation of NO

x

emissions in power plants.