Cooperative catalysis of Co single atoms and nanoparticles enables selective CAr-OCH3 cleavage for sustainable production of lignin-based cyclohexanols

In this work, a dual-size MOF-derived Co catalyst (0.2Co1-NPs@NC) composed of single atoms (Co1) and highly dispersed nanoparticles (Co NPs) was prepared by in-situ Zn evaporation for the high-performance conversion of lignin-derived o-methoxyphenols (lignin oil) to cyclohexanols (up to 97% yield) via cascade demethoxylation and dearomatization. Theoretical calculations elaborated that the dual-size Co catalyst exhibited a cooperative effect in the selective demethoxylation process, in which the Co NPs could initially dissociate hydrogen at lower energies while Co1 remarkably facilitated the cleavage of the CAr -OCH3 bond. Moreover, the intramolecular hydrogen bonds formed in the o- methoxy-containing phenols were found to result in a decrease in the bond energy of the CAr -OCH3 bond, which was more prone to be activated by the dual-size Co sites. Notably, the pre-hydrogenated intermediate (e.g., 2-methoxycyclohexanol from guaiacol) is difficult to undergo demethoxylation, indi-cating that the selective CAr -OCH3 bond cleavage is a prerequisite for the synthesis of cyclohexanols. The 0.2Co1-NPs@NC catalyst was highly recyclable with a neglect decline in activity during five consecu-tive cycles. This cooperative catalytic strategy based on the metal size effect opens new avenues for bio-mass upgrading via enhanced C -O bond cleavage of high selectivity.(c) 2023 Science Press and Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by ELSEVIER B.V. and Science Press. All rights reserved.

Automated summary

In this study, a dual-size MOF-derived Co catalyst was prepared for the conversion of lignin-derived o-methoxyphenols to cyclohexanols. The dual-size Co catalyst exhibited a cooperative effect in the selective demethoxylation process. The catalyst showed high recyclability and the cooperative catalytic strategy opens new avenues for biomass upgrading.