Enhanced catalytic oxidative depolymerization of lignin to aromatic compounds by activated carbon-supported polyoxometalate-ionic liquid catalysts

Abstract

Lignin, a major component in renewable plant biomass, serves as a potential source of high-value aromatic chemicals. However, efficiently decomposing lignin while maintaining its aromaticity for fossil fuel substitution remains a significant challenge. This study synthesized a [VimAm]Br@POM@AC catalyst, composed of a Keggin-type polyoxometalate (POM) modified by ionic liquid ([VimAm]Br) and supported on activated carbon (AC). The response-surface methodology was applied to explore the catalytic performance of this catalyst in the oxidative depolymerization of lignin β-O-4 model compounds. Under the reaction conditions of 160 °C, 3 mL H₂O₂, and 0.4 g catalyst within 8 h, the conversion rate of lignin model compounds reached 83.01 %. The reaction generated diverse aromatic products, with the selectivity of methyl mandelate and methyl benzoate reaching 27.70 % and 59.02 %, respectively. Mechanistic studies revealed that the [VimAm]Br@POM@AC catalyst selectively cleaves CO bonds in β-O-4 dimers, facilitating the formation of aromatic compounds. Moreover, FT-IR spectroscopy and SEM analysis confirmed the good stability of the recovered catalyst. This work achieves efficient directional conversion of lignin model compounds through the design of a multilevel-structured catalyst, precise optimization of reaction conditions, and innovative mechanistic interpretation. It offers a novel strategy with both academic significance and application potential for the high-value utilization of biomass resources.

Keywords: Aromatic products; Keggin-type polyoxometalate; Lignin depolymerization.