Lignin-tailored fabrication of Ni single atom catalyst with Ni-N3 active site for efficient and selective catalytic transfer hydrogenation of lignin-derived aldehydes

Developing sustainable catalytic processes for catalytic transfer hydrogenation (CTHDO) of lignin-derived aldehydes to renewable fuels and chemicals is essential for scale valorization of vast underused lignin. Herein, the work contributes to the efficient and selective vanillin (VAN) CTHDO process using formic acid (FA) as the Hdonor over a novel lignin-coordinated N-anchoring Ni single-atom catalyst (Ni SAs-N@LC). Ni SAs-N@LC was fabricated through facile pyrolysis of lignin-Ni/Zn complex mixed with melamine, in which lignin localized the Ni atoms through its negatively charged groups (e.g. phenolic OH) and the dispersed Ni atoms were further anchored by the N-doped carbon support to form Ni-N3 active structure. DFT calculations revealed that the Ni-N3 structure preferentially adsorbed the -CHO end of VAN and endowed the catalyst with superior hydrogen evolution capacity. Therefore, Ni SAs-N@LC exhibited outstanding catalytic performance (98.93% of VAN conversion and 97.3% of 2-methoxy-4-methylphenol selectivity) which was significantly higher than two reference catalysts Ni NPs@LC (without N-anchoring) and Ni@C (without lignin coordination and N-anchoring) as well as the previously reported Ni-based catalysts. Moreover, Ni SAs-N@LC presented excellent feasibility to the CTHDO of a wide range of lignin-derived aldehydes and exhibited superior cycling durability in FA system owing to its acid resistance property. Consequently, this work provides a facile preparation method for atomically dispersed biomass-based catalysts and further demonstrates its favorable applicability in the CTHDO of lignin-derived aldehydes.