The impact of H-ZSM-5 catalyst on the mechanism of fuel-N conversion during glutamic acid pyrolysis

Abstract

During the pyrolysis of biomass, Fuel-bound Nitrogen (Fuel-N) is converted into N-containing compounds present in bio-oil and biochar. These compounds are easily oxidized into NOx during subsequent utilization, causing ecological damage. Catalytic fast pyrolysis has emerged as a promising method for denitrogenation in recent years, but the underlying catalyst mechanism still needs to be determined. This study analyzed the impact of catalyst H-ZSM-5 on the mechanism of Fuel-N conversion during the pyrolysis of glutamic acid, a model compound for nitrogenous biomass, through experimental studies and theoretical calculations. According to literature data, the pyrolysis of glutamic acid predominantly yielded the N-containing products pyrrole, glutarimide, and pyrrolidone. The H-ZSM-5 catalyst showed optimum denitrification at 600 ℃, resulting in a 49.62% reduction in the proportion of N-containing compounds. In the catalytic pyrolysis products, the generation of toluene and naphthalene increased. In-situ DRIFTS experiments were consistent with the results of Py-GC-MS experiments, with catalytic pyrolysis promoting deaminations and decarboxylations, decreased imines and nitriles, and increased aromatic hydrocarbons. Additionally, the energy barrier changes of each pyrolysis pathway were calculated based on Density Functional Theory (DFT). The results showed that the H-ZSM-5 catalyst primarily promoted the deamination reaction, followed by the decarboxylation and dehydration condensation reactions, while inhibiting the dehydrogenation reaction. Moreover, the energy barrier for unsaturated hydrocarbon addition reactions was reduced, facilitating the formation of aromatic compounds. The acid sites inside the H-ZSM-5 catalyst weakly interacted with the reactants, making it easier to detach the amino group during catalytic pyrolysis. This study provides a reference for the denitrification of bio-oil and biochar. Subsequent work can realize the regulation of nitrogen conversion by changing the acidity and concentration of catalyst acid sites.