Density functional theory study on the conversion path of leucine by non-thermal plasma

At present, non-thermal plasma technology has received extensive attention in the treatment of solid waste. Based on the density functional theory (DFT), the conversion path of leucine (LEU) as the model compound of protein in sludge during the non-thermal plasma treatment was simulated at the B3LYP/6-31G(d,p) level; 7 main conversion paths were considered, including the deamination priority mechanisms, decarboxylation priority mechanisms, and the remaining C−C bond breaking priority mechanisms. The results show that leucine is easy to lose the amino group and carboxyl group, generating C₅H₁₀ which is further decomposed into small molecular hydrocarbons. The CO₂ product comes from the carboxyl group; although the reaction barrier to form CO is relatively high, CO₂ is easily ionized into CO in the plasma, leading to the increase of CO concentration. The combination of small free radicals and the decomposition of other small molecules generate CH₄ and H₂. The energy required for all paths is within the maximum value of the high-energy electron energy in the non-thermal plasma.