Effects of different pretreatments on catalytic conversion of biomass to methyl levulinate over P-doped CoS2

Methyl levulinate (ML) is a high-value platform chemical with broad applications. However, its efficient production from lignocellulosic biomass is hindered by the recalcitrant matrix of cellulose, hemicellulose, and lignin. This study demonstrates a two-step strategy for converting pine to ML, which couples biomass pretreatment with subsequent catalytic depolymerization over a P-doped CoS2 catalyst. The regulatory mechanisms of three distinct pretreatments, including dilute acid washing, H2O2 peroxidation, and alkaline extraction, on the physicochemical structure of pine were systematically investigated. The ML yield increased from 0 (untreated pine) to 2.6 wt% after acid washing, 7.3 wt% after peroxidation, and exceeded 17 wt% following alkaline extraction with 5 wt% NaOH. The enhancement is attributed to a synergistic mechanism whereby pretreatments not only improve biomass accessibility but also crucially eliminate compounds that poison the catalytic active sites. Acid washing removes ash components, mitigating the poisoning of Lewis acid sites on the catalyst. Peroxidation and alkaline extraction disrupt the lignin-carbohydrate complex, removing lignin-derived phenolics that cause catalyst deactivation. However, excessive oxidant or alkali concentrations degrade the cellulose structure, leading to yield attenuation. This work confirms that selecting an appropriate pretreatment is paramount to balancing component removal for the efficient valorization of pine into ML.