Catalytic Effect of Alkali and Alkaline Earth Metals in Lignin Pyrolysis: A Density Functional Theory Study

Catalytic pyrolysis is a promising technology for the production of renewable fuels and chemicals from lignin. The yield of aromatic compounds from the catalytic pyrolysis of lignin is significantly affected by the naturally existing alkali and alkaline earth metals (AAEMs). Through extensive density functional theory study, we investigated, at the molecular level, the influence of AAEMs on the bond breaking mechanism of representative lignin model compounds. According to the calculation results, AAEMs were found to strongly bind with O(Cβ) and O(methoxy), and the catalytic activities of AAEMs were correlated with their electronegativities. This prediction was proved by calculating the stabilization energy, half-sandwich structure, and elongated bond length of Cβ–O along with the Wiberg bond order. Importantly, our findings provide a significant insight for understanding the effect of naturally occurring AAEMs on the catalytic pyrolysis of lignin.