A comprehensive study of indole catalytic hydrodenitrogenation under hydrothermal conditions

This article focuses on the catalytic hydrodenitrogenation (HDN) mechanism of indole under hydrothermal conditions. Formic acid (FA), which is a donor of both gaseous hydrogen and liquid hydrogen, can improve indole conversion and total yield of denitrogenated products. Ru/C showed the highest activity among the catalysts in this study for indole conversion at all temperature conditions with the existence of H₂, and 91.17% indole was converted at 400°C and 60 min. Based on reaction kinetic experiments, a kinetic model was developed mathematically to describe the hydrothermal HDN reaction of indole over the home-made Ni₈₀Ru₂₀/γ-Al₂O₃ catalyst, which clearly captured all data trends and fitted the temporal variation of all major liquid products. High activation energy for the formation of the O-containing substance o-cresol from both mathematical fitting and density functional theory (DFT) calculation indicated the rare occurrence of a reaction between the pyrrole ring-opening product methyl aniline and H₂O, consistent with the experimental observation that only a trace of o-cresol was detected.