Frustrated Lewis Pairs and Metallic Ni Synergistically Enabled Low-Temperature Hydrogenolysis of Lignin Models

Low-temperature hydrogenolysis of aromatic ether bonds is a highly promising strategy to convert lignin. However, it remains highly challenging to enable this strategy over non-noble metal-based catalysts. Herein, Ni and Al mixed oxide catalysts (denoted as NiAlO_x-T, where T represented the reduction temperature) were constructed by the reduction of layered Ni-Al hydroxides. Interestingly, the NiAlO_x-300 could efficiently promote the hydrogenolysis of various lignin models (i.e., α-O-4 referring to benzyl phenyl ether linkage (C_α-O-Ar), β-O-4 referring to 2-phenoxy-1-phenylethanol linkage (C_β-O-Ar), and 4-O-5 referring to diphenyl ether linkage (Ar-O-Ar)) at a temperature of ≤ 100°C. Notably, benzyl phenyl ether (a typical α-O-4 model) could be converted into toluene and phenol at 20°C. Systematic analysis revealed that abundant solid surface frustrated Lewis pairs (ssFLPs) composed by unsaturated Al sites (Al³⁺ _unsatur.) proximal to a surface oxygen vacancy and surface Lewis basic OH were generated in NiAlO_x-300. The excellent performance of the NiAlO_x-300 catalyst originated from the synergistic effect of ssFLPs sites and metallic Ni⁰ sites, which was beneficial to efficient hydrogen activation for hydrogenolysis of lignin models at mild conditions. This work provided a new kind of non-noble metal-based catalyst for lignin valorization by creating solid surface frustrated Lewis pairs cooperated with non-noble metals.