Catalytic Hydrodenitrogenation of Pyridine under Hydrothermal Conditions: A Comprehensive Study

Abstract

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.

CO2 reduction into formic acid under hydrothermal conditions: A mini review

“…Except for the potential hydrogen source and promoter, water could serve as a reactant to produce hydrogen and alcohol, aldehyde, acid and other oxygen‐containing derivatives in the hydrothermal liquefaction of polyethylene to oil 43,44 . Similarly, Guo and Luo et al 45,46 also found H 2 O in the hydrothermal conditions could directly participate in hydrodenitrogenation reactions of nitrogen‐containing heterocyclic substances, in which the oxygen‐containing compounds were generated from the interaction with water.…”

A comprehensive study of indole catalytic hydrodenitrogenation under hydrothermal conditions

“…Our recent research has shown that FA, acting as a hydrogen source, can promote the HDN reaction of the nitrogen heterocyclic ring chemical pyridine under hydrothermal conditions with a Ni-Ru bimetallic catalyst. 14 Apart from an external hydrogen source such as H 2 and FA, high-temperature, high-pressure (HTHP) water (250-400 C, 5-25 MPa) itself is a potential hydrogen source as well because of its unique inherent property of high ionic product (K w ) and low dielectric constant. 15 In this case, H 2 could be in situ generated from the radical reaction under hydrothermal condi- 16 Wang et al 17 found that HTHP H 2 O can also act as a bridge for methanol activation and oxidation to produce in situ H 2 and thereby achieve HCO 3 À reduction.…”

“…Although some studies have demonstrated that H 2 O could serve as an environmentally benign solvent, it would introduce O into the biooil phase during hydrothermal HDN reactions. 14,18 Luo et al 19 pointed out two pathways to achieve HDN under hydrothermal conditions:…”

“…Savage et al 13 found that formic acid (FA) could be completely decomposed at 341°C under hydrothermal condition within 41 s and the in situ H 2 selectivity reached 100%. Our recent research has shown that FA, acting as a hydrogen source, can promote the HDN reaction of the nitrogen heterocyclic ring chemical pyridine under hydrothermal conditions with a Ni–Ru bimetallic catalyst 14 . Apart from an external hydrogen source such as H 2 and FA, high‐temperature, high‐pressure (HTHP) water (250–400°C, 5–25 MPa) itself is a potential hydrogen source as well because of its unique inherent property of high ionic product ( K w ) and low dielectric constant 15 .…”

“…In a hydrodeoxygenation (HDO) study, Miao et al 17 found that the deoxygenation yield of palmitic acid was 1.8% without water and 35.5% with water over Ni/ZrO 2 at 300°C for 6 h, and they attributed this improvement to the in situ H 2 formation in the presence of water. Although some studies have demonstrated that H 2 O could serve as an environmentally benign solvent, it would introduce O into the bio‐oil phase during hydrothermal HDN reactions 14,18 . Luo et al 19 pointed out two pathways to achieve HDN under hydrothermal conditions: (1) hydrocarbons are directly produced from the indole HDN reaction, and (2) intermediate oxygenated products from the hydrolysis of partial hydrogenation of indole are hydrodeoxygenated to remove O to obtain hydrocarbons.…”