Theoretical study on the effect of H2O on the formation mechanism of NOx precursors during indole pyrolysis

The incineration technology of kitchen waste is one of the effective technologies to achieve the resource utilization of municipal solid waste. Pyrolysis is an important stage of incineration. Indole is a rich initial product in the pyrolysis process of kitchen waste, and the presence of H₂O has a significant impact on the decomposition of indole to form NO_x precursors. Therefore, this study uses density functional theory method to study the effect of H₂O on the thermal decomposition of indole to produce NH₃, HNCO, and HCN. When H₂O participates in the reaction, it can provide oxidative groups to generate a new product HNCO, which is different from the previous findings by indole pyrolysis without the presence of H₂O. Meanwhile, this study theoretically proves that NH₃ is easier to form than HCN. This is consistent with the phenomenon that NH₃ release is higher than HCN release in pyrolysis experiment. In addition, compared with the individual pyrolysis of indole, the participation of H₂O reduces the energy barriers for the formation of NH₃ and HCN during indole pyrolysis, thereby promoting the formation of NH₃ and HCN.