Products, pathways, and kinetics for catalytic hydrodenitrogenation of quinoline in hydrothermal condition

The purpose of this study is to investigate reaction mechanism and kinetics of catalytic hydrodenitrogenation (HDN) of quinoline under hydrothermal conditions (300 °C, 350 °C, and 400 °C), using Ni-Ru/γ-Al₂O₃ catalyst and formic acid (FA) as hydrogen donor. 1,2,3,4-tetrahydroquinoline, decahydroquinoline, aniline, methyl aniline, 2-hexene, and toluene were primary products. Quinoline conversion fits a first-order kinetics, with an activation energy of 41.72 kJ/mol. A possible reaction network of HDN of quinoline was developed and the corresponding kinetic model captures nearly all the temporal variation of all major products’ concentration. The kinetic modeling results indicated that the dehydrogenation of 1,2,3,4-tetrahydroquinoline to quinoline is the rate-determining step with high energy barrier of 174.6 kJ/mol. Reaction rate analysis showed 2-hexene as the major denitrogenated product is mainly derived from hydrogenation of aniline and its formation rate from decahydroquinoline is higher than the path from aniline derivatives. Sensitivity study revealed that hydrogenation from quinoline to decahydroquinoline has a strong influence on the whole reaction process. Both catalyst durability test and catalyst characterizations demonstrated that the Ni-Ru bimetallic catalyst was relatively unstable under supercritical water conditions, probably due to the joint influences of partial agglomeration of active metal and hydrolysis of supporter γ-Al₂O₃.