Base-free aerobic oxidative cleavage of C–C bonds in lignin by dual-active-site regulation of CoOx@MCM-41-Co catalyst

C β –H and oxygen activation are both critical during oxidative lignin depolymerization. Usually, a base is needed to promote the reaction. In this study, a series of CoO x @MCM-41-Co-n catalysts were developed, in which the ratio of the dual active sites (CoO x and Co–O–Si) can be simply regulated by changing the timing of silicon source addition, enabling selective base-free C–C oxidative cleavage of the β -O-4 linkage in a lignin model compound using a low cobalt content (1.5 wt%). The dual active sites cooperate to achieve high yields of phenol (80.41%) and benzoic acid (80.43%), and the reaction rate reached 166.67 mmol· g cat ( Co ) − 1 ·h -1 . A mechanistic study reveals that the CoO x site promotes 1 O 2 formation to improve oxygen activation ability, while the Co–O–Si site mainly enhances C β –H activation, avoiding additional base usage. In addition, the catalytic system is applicable to various methoxy - substituted β -O-4 model substrates and organosolv birch lignin. This study provides new insights into the design of catalysts for the oxidative depolymerization of lignin.