Mechanistic insights into lignin catalytic hydropyrolysis: Role of nickel catalyst and hydrogen

Lignin catalytic hydropyrolysis has garnered significant interest for its potential to convert lignin into valuable biofuels and chemicals. However, the underlying mechanisms of this process, particularly the role of catalysts and hydrogen influence reaction pathways and product distribution, has not yet been fully elucidated. This study aims to address these gaps by investigating the mechanism of lignin catalytic hydropyrolysis with a nickel catalyst, employing both experimental and simulation approaches. Experimental results demonstrated that the catalyst effectively promoted demethylation and hydrodeoxygenation, with increased hydrogen pressure further facilitating C-O bond cleavage and enhancing hydrodeoxygenation. Simulation results revealed that both the catalyst and elevated temperature promoted C-C and C-O bond cleavage in lignin, accelerating reactant decomposition and the formation of light weight products. It was found that while a moderate increase in hydrogen pressure facilitated hydrodeoxygenation of liquid products, excessive pressure suppressed bond cleavage, thereby hindering further enhancement of liquid product quality. Notably, the simulations provide direct evidence that high-pressure hydrogen mitigates catalyst deactivation by suppressing carbon accumulation. This study highlights the complex interplay between temperature, hydrogen molecules, and the catalyst during lignin catalytic hydropyrolysis. This approach offers insights into lignin catalytic hydropyrolysis and supports the development of efficient catalysts for biomass conversion.