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

Abstract

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.