Theoretical Investigation of the Formation Mechanism of NH(3) and HCN during Pyrrole Pyrolysis: The Effect of H(2)O

Coal is a major contributor to the global emission of nitrogen oxides (NO(x)). The NO(x) formation during coal utilization typically derives from the thermal decomposition of N-containing compounds (e.g., pyrrolic groups). NH(3) and HCN are common precursors of NO(x) from the decomposition of N-containing compounds. The existence of H(2)O has significant influences on the pyrrole decomposition and NO(x) formation. In this study, the effects of H(2)O on pyrrole pyrolysis to form NO(x) precursors HCN and NH(3) are investigated using the density functional theory (DFT) method. The calculation results indicate that the presence of H(2)O can lead to the formation of both NH(3) and HCN during pyrrole pyrolysis, while only HCN is formed in the absence of H(2)O. The initial interaction between pyrrole and H(2)O determines the N products. NH(3) will be formed when H(2)O attacks the C(2) position of pyrrole with its hydroxyl group. On the contrary, HCN will be generated instead of NH(3) when H(2)O attacks the C(3) position of pyrrole with its hydroxyl group. In addition, the DFT calculations clearly indicate that the formation of NH(3) will be promoted by H(2)O, whereas the formation of HCN is inhibited.