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

Abstract

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, indicating 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 consecutive cycles. This cooperative catalytic strategy based on the metal size effect opens new avenues for biomass upgrading via enhanced C O bond cleavage of high selectivity.