Catalytic Hydrodenitrogenation of Pyridine under Hydrothermal Conditions: A Comprehensive Study

This article focuses on the kinetic modeling and catalytic performance of hydrodenitrogenation of pyridine under hydrothermal conditions. Piperidine derivatives are the major nitrogen-containing intermediates, including 1-piperidinecarboxaldehyde, 1-piperidineethanol, and alkyl piperidines. Catalysts overall improved the formation of N-free products including 1-pentanol and 2-methyl-1-pentanol. Commercial Pd/C provided the highest pyridine conversion rate at 350 °C, while the homemade Ni-Ru bimetallic catalyst provided a prominent denitrogenation activity at 400 °C, leading to the highest 1-pentanol yield as a major denitrogenated product. Conversion of pyridine over the Ni50Ru50/C catalyst led to formation of three major alkyl piperidines (1-ethyl piperidine, 1-methyl piperidine, and 1-pentyl piperidine). These alkyl piperidine intermediates could further be converted into amino and N-free compounds. A kinetic model was developed to mathematically describe the hydrothermal HDN reaction of pyridine over the Ni50Ru50/C catalyst, which clearly captured all data trends and fitted the temporal variation of all major products. Sensitivity analysis suggested that dehydrogenation from piperidine to pyridine has a strong impact on the whole reaction pathways.