Study on the thermal regeneration mechanism of ammonia-modified activated coke for the synergistic removal of NO and Dioxins

Activated coke is considered as a promising multifunctional adsorbent and catalyst for the simultaneous removal of multiple flue gas pollutants, and the regeneration performance directly determines its engineering feasibility and economic benefits. To achieve efficient regeneration and sustainable recycling of activated coke after the synergistic removal of nitric oxide (NO) and o-dichlorobenzene (o-DCB), ammonia-modified activated coke (600NAC) after co-adsorption saturation was used as the research object. A series of regeneration experiments were conducted in a fixed-bed reactor, and the effects of regeneration temperature (400-700℃) and regeneration atmosphere (N2, NH3) on regeneration efficiency, pollutant degradation pathways, surface chemical properties and pore structure evolution of activated coke were systematically studied. Advanced characterization methods including gas chromatography-mass spectrometry (GC-MS), Fourier transform infrared spectroscopy (FTIR), Brunauer-Emmett-Teller (BET) specific surface area analysis, X-ray photoelectron spectroscopy (XPS) and temperature-programmed desorption of oxygen (O2-TPD) were adopted to reveal the regeneration mechanism, analyze the physicochemical property changes and clarify the pollutant transformation pathways. The experimental results demonstrate that regeneration temperature and atmosphere play decisive roles in the recovery of adsorption capacity and cyclic stability. The regeneration effect under NH3 atmosphere is significantly better than that under N2 atmosphere for NO adsorption. At the optimal temperature of 600℃, NH3 regeneration restores the NO adsorption capacity to 46.21 mg/g, which exceeds that of the original 600NAC sample, and 95% of the initial removal performance can be maintained after five consecutive adsorption-regeneration cycles. For o-DCB adsorption, high-temperature regeneration at 600-700℃ promotes the decomposition of pollutants and the reconstruction of active sites, thus effectively restoring the adsorption performance. The o-DCB adsorption capacity reaches 89.65 mg/g after regeneration at 600℃ in NH3 atmosphere, and more than 80% of the capacity is retained after five cycles, showing excellent cyclic stability. Regeneration treatment significantly modifies the physical and chemical properties of activated coke. N2 regeneration is conducive to the recovery of specific surface area and pore volume, with the maximum BET surface area of 663.53 m2/g obtained at 500℃. Although NH3 regeneration slightly reduces the specific surface area due to the loading of nitrogen-containing species, it optimizes the pore structure distribution and enhances surface chemical activity. N2 regeneration causes continuous loss of nitrogen-containing functional groups with increasing temperature, while NH3 regeneration enriches nitrogen functional groups on the surface in the range of 400-600℃. The total nitrogen content reaches 1.42% at 600℃, with quaternary nitrogen accounting for 49%, which greatly improves the surface activity and adsorption selectivity. O2-TPD results confirm that NH3 regeneration at 600℃ promotes the formation of chemisorbed oxygen and surface lattice oxygen, providing active sites for pollutant adsorption and catalytic degradation. The regeneration atmosphere effectively regulates the degradation mechanism and reaction pathways of o-DCB. In N2 atmosphere, regeneration is dominated by thermal desorption and depolymerization. At 400-500℃, o-DCB is desorbed and partially dechlorinated to form chlorobenzene. At 600℃, chlorinated aromatic rings undergo condensation reactions to produce complex macromolecular by-products, increasing the risk of dioxin precursor formation. At 700℃, intermediates are completely decomposed into HCl. In NH3 atmosphere, NH3 participates in the regeneration reaction through chemical interaction, promoting the cleavage of C-Cl bonds and strengthening the dechlorination process. It inhibits the condensation of chlorinated aromatics, reduces the risk of secondary dioxin formation and lowers the release of chlorine in the form of HCl. However, the degradation of o-DCB consumes hydroxyl and nitrogen-containing functional groups, leading to a slight decline in partial performance after regeneration. This study clarifies the synergistic regulation mechanism of regeneration temperature and atmosphere on activated coke regeneration, and proves that 600℃ and NH3 atmosphere is the optimal condition, which not only efficiently restores the adsorption capacity of NO and o-DCB but also maintains excellent long-cycle stability and low secondary pollution risk. The research results provide important theoretical support and technical reference for the efficient regeneration and industrial application of activated coke in the synergistic control of flue gas pollutants.