Co3O4 undergoes in situ reduction to mediate lignin hydrodeoxygenation under mild conditions with high liquid yield and recyclability

Abstract

Lignin, due to its structural rigidity, tends to form coke deposits during catalytic hydrodeoxygenation (HDO), causing catalyst deactivation, and eliminating coke to restore performance is challenging. In this study, Co₃O₄ shows excellent HDO performance toward lignin model dimers, with high selectivity for demethoxylation and deethoxylation under mild conditions via a one-step strategy integrating in situ reduction and HDO, thereby enabling lignin HDO. At 240 °C, 2 MPa, and 20 h, lignin achieved a 73% liquid yield, with 64%, 30%, and 6% selectivities to alkanes, alcohols, and phenols. This is attributed to Co₃O₄'s high Co–O bond energy, dominant (220) crystal plane exposure, and high Co³⁺/Co²⁺ ratio, facilitating in situ reduction to metallic cobalt active sites. Coke on Co₃O₄ can be removed by calcination to restore performance, with 90% of the initial liquid yield retained after five cycles. This low-cost commercial non-noble metal Co₃O₄ enhances the economic feasibility of lignin's high-value utilization.