Defect Engineering-Regulated Electron Transfer of NiAl-MMO for Catalyzing Directed Conversion of Lignin into Cyclohexanol-Based Chemicals

Abstract

Regulating electron transfer through defect engineering to selectively catalyze the cleavage of lignin C–O bonds is of significant scientific importance for the directed conversion of biomass into high-value chemicals. However, the precise dissociation of chemical bonds remains challenging. In this study, a 2D nanoflower-like NiAl-MMO catalyst was successfully constructed via a hydrothermal in situ pyrolysis synergistic strategy. An Al doping strategy was employed to fabricate Ni and Al³⁺-O_v (O_v denotes oxygen vacancy) synergistic dual active centers in NiAl-MMO. The research results indicate that the introduction of Al significantly enhances the catalytic performance. When an appropriate amount of Al is doped, it not only effectively increases the specific surface area of the catalyst and optimizes its pore structure but also enables the formation of moderate-strength interactions between metallic Ni and Al. Meanwhile, the presence of Al induces an increase in the concentration of O_v in the catalyst. O_v can regulate the electronic state of Ni active sites by modulating electron density while also enhancing the Lewis acidity of the catalyst, thereby improving its adsorption capacity for reactants. This electronic regulation optimized the electronic coupling environment of bimetallic sites and significantly strengthened the synergistic effect between Al³⁺-O_v and Ni sites, improving the hydrogen activation capability and directed C–O bond cleavage performance of the catalytic system. The catalyst exhibited excellent C–O bond dissociation selectivity in the lignin hydrodeoxygenation (HDO) process with a total liquid yield of 45.7 wt % (68.4% selectivity for C₆₊ cyclohexanol), providing a new approach for the synthesis of aviation fuel precursors. This work offers a novel strategy for the directed conversion of lignin through the synergistic regulation of interfacial defects and electronic structures.