Crystalline porous materials for catalytic conversion of lignin-related substances

The conversion of the biomass into eco-friendly fuels and chemicals has been extensively recognized as the essential pathway to achieve the sustainable economy and carbon neutral society. Lignin, as a kind of promising biomass energy, has been certified to produce the high-valued chemicals and fuels. Numerous efforts have been made to develop various catalysts for lignin catalytic conversion. Both metal-organic frameworks (MOFs) and covalent organic frameworks (COFs) belong to very important heterogeneous porous catalysts due to their regular porous structures, high specific surface area, and precisely tailored diversities. In the review, the first part focused on the catalytic conversion of lignin, lignin model compounds, and lignin derivatives using the pristine MOFs, functional MOF composites, and MOF-derived materials. The second part summarized the catalytic conversion of lignin model compounds using pristine COFs and functional COF composites. The review here mainly concentrated on the design of the materials, screening of catalytic conditions, and explorations of the corresponded mechanisms. Specifically, (1) we summarized the MOF- and COF-based materials for the effects on the catalytic transformation of lignin-related substances; (2) we emphasized the catalytic mechanism of C-C and C-O bonds cleavage together with the structure-activity relationships; (3) we in-depth realized the relationship between the chemical/electronic/structural properties of the MOF- and COF-based catalysts and their catalytic performance for lignin-related substances. Finally, the challenges and future perspectives were also discussed on the catalytic conversion of lignin-related substances by MOF- and COF-based catalysts. Efficiently converting renewable lignin into valuable chemicals and fuels holds great significance in solving energy crises and mitigating global warming. Based on the high specific surface area, controllable structures and pores, functionalized overall frameworks, and designable catalytic sites, the rational design of MOF- and COF-based catalysts is a promising way to achieve conversion of lignin-related substances. image