Effects of ammonia-coal co-pyrolysis on heterogeneous reduction of NO: Quantum chemical calculations and pyrolytic reduction experiments

Abstract

Ammonia-coal co-combustion is a promising technology for reducing carbon dioxide emissions. However, the mechanism by which nitrogen-containing functional groups in the post-flame zone influence carbon during the co-combustion process is unclear. In this study, it is assumed that -NH₂ groups enhance nitrogen monoxide reduction by activating the char surface. Quantum chemical calculations, pyrolysis reduction experiments and X-ray Photoelectron Spectroscopy (XPS) experiments were combined to investigate -NH₂ modified char's reactivity. Quantum calculations show that the -NH₂ group activates the char surface, effectively enhancing the NO reduction on the char, with advantages in both thermodynamics and kinetics. Additionally, the calculations reveal that both -H and -NH (further pyrolysis products of -NH₂) can also lower the energy barrier for NO reduction on the char. The pyrolysis reduction experiment results show that increasing the co-pyrolysis temperature and ammonia blending ratio enhances the char's ability to reduce NO. Further XPS experiments reveal that the NO reduction rate exceeds the rate of decrease of char-NH₂, and this characteristic becomes more pronounced with increasing ammonia concentration during the co-pyrolysis stage. This confirms that the surface heterogeneous reduction of NO on char-NH₂ is an important pathway in the absence of -NH₂ involvement in the reaction.