Mechanism investigation of the effect of coal gangue composition on the conversion of ammonia and nitric oxide on its surface

Ammonia (NH3) has emerged as a zero-carbon fuel that can be co-firing with coal. This co-firing practice offers a dual advantage: it reduces carbon emissions to some extent while also enhancing the utilization rate of low-calorific-value fuels such as coal gangue. In this study, we investigated the adsorption and conversion of NH3 in coal gangue under different atmospheres and temperatures and its influence on NO reduction by means of a fixed-bed reaction system and characterization methods such as SEM, XRD and XPS. Findings reveal that under the atmosphere containing only NH3 and N2, the higher content of Fe2O3 and organic components in Changzhi gangue (CS) leads to heightened conversion activity of NH3. Of these, NO will be produced as a byproduct of the reaction between NH3 and the oxygen in the coal gangue. Under the coexistence of NH3 and O2, CS had a surface adsorbed O content of 67.47 %, which exceeded that of PS. The oxidation reaction of NH3 was contributed by the surface acidic sites of CS with different active ingredients and the synergistic effect of chemisorbed O. As a result, the CS outlet had a higher NH3 conversion (96.86 %) and NO selectivity (99.15 %) than the PS outlet. Under the coexistence of NH3 and NO, the NO reduction efficiency of CS reaches 99.98 % at 850 °C, and the ability of NO to oxidize NH3 is weaker than the ability of O2. Under the coexistence of NH3, NO and O2, the oxidation of NH3 gradually dominated with increasing temperature and led to the production of additional NO. •Higher Fe2O3 and organic components in gangue increased NH3 conversion activity.•Gangue promotes NH3 decomposition and its oxygen content partly oxidizes NH3.•Activated gangue achieves 96.86 % NH3 conversion when NH3 and O2 coexist.•At 850 °C NH3 achieves a 99.98 % NO reduction rate with Activated gangue.•O2 promotes the catalytic oxidation of NH3 on coal gangue with or without NO.