A theoretical investigation on the thermal decomposition of pyridine and the effect of H2O on the formation of NOx precursors

Pyridine is one of the main nitrogen-containing compounds in coal, and its pyrolytic mechanism to generate NO_x precursors (mainly NH₃ and HCN) remains unclear. In this work, the possible pathways for the pyrolysis of pyridine to form HCN and/or NH₃ were investigated by the density functional theory method, and the effects of H₂O on pyridine pyrolysis were also investigated. The results show that there are two possible reactions for the initial pyridine pyrolysis, i.e., internal hydrogen transfer and C–H bond homolysis, and that internal hydrogen transfer is more favorable. Nine possible reaction pathways following internal hydrogen transfer are obtained and analyzed. Among these pathways, pyridine prefers to produce HCN instead of NH₃. The existence of H₂O has significant effects on the decomposition of pyridine, as it participates in pyridine pyrolysis to form NH₃ rather than HCN as the major product.