Efficient Metal-Acid Bifunctional Catalysts Derived from NiAl-LDO for the Reductive Catalytic Fractionation of Lignocellulose into Phenolic Monomers

Reductive catalytic fractionation (RCF) is a promising lignin-first strategy to produce valuable phenolics from lignocellulosic biomass. However, this method encounters the challenges of a low yield of phenolic monomers and the use of expensive noble metal catalysts. In this study, a reduced NiAl layered double oxide (NiAl-LDO) catalyst is reported for the RCF of lignocellulosic biomass with high depolymerization efficiency and phenolic monomer yields. The RCF reaction of pine at 260 °C yielded 27.49 wt % of lignin oil and 21.62 wt % of phenolic monomers, with a delignification degree of 92.62%. In addition, high-performance liquid chromatography analysis showed that the solid carbohydrate pulp fraction retained up to 80.63% cellulose, which can be used as an economical feedstock for the production of other platform chemicals. Further characterization and mechanistic studies including NH3-TPD, Py-FTIR, and 2D HSQC NMR revealed that the strong acidic sites derived from Ni2+ at the metal–support interface play a crucial role in promoting the hydrogenolysis of aryl ether bonds within lignin, thereby significantly improving the yield of phenolic compounds. Understanding the role of the NiAl-LDO catalyst acidity in the RCF reaction is beneficial for the production of phenolic products from biomass based on a lignin-first strategy.