Co 3 O 4 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, Co 3 O 4 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, and enables lignin HDO. At 240 o 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 Co 3 O 4 's high Co-O bond energy, dominant (220) crystal plane exposure, and high Co 3+ /Co 2+ ratio, facilitating in-situ reduction to metallic cobalt active sites. Coke on Co 3 O 4 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 Co 3 O 4 enhances the economic feasibility of lignin's high-value utilization.IntroductionLignin, accounting for 15-30 wt% of lignocellulose, is the most abundant renewable aromatic resource on earth, holding immense potential to replace fossil feedstocks in producing high-value