Ni-substituted POM@UIO-66 catalyst for high-efficiency catalytic conversion of larch lignin

Abstract

Converting abundant lignin resources into high-value chemicals has always been a pivotal approach in biomass refining. Among various methods, catalytic oxidative depolymerization stands out as one of the most promising approaches due to its mild reaction conditions and remarkable efficiency. In this study, we present a series of transition metal-substituted Ni/Co-PMo/PW@UIO-66 catalysts, among which NiPMo@UIO-66 demonstrated the superior catalytic performance after thorough characterization. Through more in-depth research, it was found that under the optimal reaction conditions of 160 °C, 1.0 MPa O₂, and 3 h, the strong Brønsted acidity inherent in POM, combined with the excellent redox properties, the moderate Lewis acidity provided by Ni and Zr, and the improved substrate-catalyst interfacial contact offered by the UIO-66 carrier, synergistically yielded the formation of the high amount of primary products and outstanding selectivity (>90 %). Therefore, the optimal yields of vanillin and methyl vanillate reached 11.26 wt%. Additionally, reusability experiments demonstrated that UIO-66 ensures its recyclability, with the NiPMo@UIO-66 catalyst exhibiting excellent catalytic activity over 5 cycles, albeit with a slight decline in the yield of aromatic monomers. In terms of stability, the POM undergoes partial decomposition after multiple uses, while the UIO-66 framework maintains remarkable stability. This study aims to provide insightful and inspiring contributions to the design of catalysts within the lignin catalytic oxidative valorization system.