Mechanism of micro‑oxygen rapidly modified reburning fuel for NOx reduction in fast load regulation

Nitrogen oxides (NOx) emissions increase sharply during variable-load operation, creating an urgent need for low-cost NOx control technologies. This study proposes a rapid modification strategy for reburning fuel using a small circulating fluidized bed. By introducing trace O 2 into a CO 2 atmosphere, the effects of micro‑oxygen modification on coal char's pore structure, carbon skeleton defects, and surface functional groups were systematically investigated. Combined with temperature-programmed NO reduction experiments and density functional theory (DFT) calculations, the regulatory mechanism was elucidated. Results show that extending the residence time to 5 min, coupled with the introduction of 1% O 2 , promotes deep volatile cracking andsignificantly increasing CO yield in pyrolysis gas. Synergistic O 2 -CO 2 gasification facilitates micropore development and defect formation, enriching C O functional groups and reactive nitrogen structures to generate abundant C-N-O active sites. The char prepared under the optimal condition (Case5) achieves an approximately 53% increase relative to the CO 2 only baseline (Case1). DFT calculations reveal the transformation pathways of nitrogen-containing groups, with the dominant pathway exhibiting lower activation energy barriers, elucidating the microscopic mechanism of char activation. This work provides theoretical basis for rapid preparation of coal-based deNOx materials under variable-load conditions.