Enhanced reductive catalytic fractionation of lignocellulose using a water-resistant RuNiZnO_x/Nb₂O₅ catalyst with synergistic hydrogen spillover and acidic properties

Eco-friendly lignin depolymerization into monomeric phenols in an aqueous system is essential for the sustainable and green valorization of lignocellulosic biomass. However, a major challenge in this process is the development of efficient and stable catalysts for aqueous reductive catalytic fractionation (RCF), as water can cause catalyst deactivation and reduce monomer yields. In this study, a water-resistant RuNiZnO_x/Nb₂O₅ catalyst is developed that demonstrates excellent catalytic activity and stability in aqueous systems, achieving a near-theoretical monomeric phenol yield of 40.1 wt% under reaction conditions of 240℃ and 3 MPa H₂ for 4 h. The excellent performance of this catalyst is attributed to the synergistic hydrogen spillover effect between Ni and Ru and the strong acidic properties of ZnO, as revealed by in-situ XPS analysis and NH₃-TPD, respectively. This hydrogen spillover effect significantly alters the product composition, promoting the generation of POH-S/G from lignin model compounds. Additionally, screening of the catalyst support materials revealed that Nb₂O₅ not only enhances Ru dispersion but also improves its stability, resulting in a minor decrease in lignin monomer yield observed after three cycles.