Activating MnO with Embedded Ru for Enhanced Selective Hydrogenolysis of C–O Bonds in Lignin-Derived Ethers over Ru–MnO/Al2O3

While C–O bond cleavage is pivotal in the depolymerization/valorization of lignin, it is still challenging to control the reaction selectivity under high activity due to the higher dissociation energy of aromatic C–O bonds relative to other reactions such as direct ring hydrogenation. Herein, we report the activation of Al2O3-supported earth-abundant MnO with embedded Ru to enhance the selective hydrogenolysis of aromatic C–O bonds in both a model compound and real lignin. Complementary characterizations demonstrate that the embedment of Ru into the MnO phase generates vacancy-enriched MnO under a hydrogen atmosphere, and such abundant active sites enable about threefold enhancement of the specific reaction rate for C–O bond hydrogenolysis. Moreover, the defective MnO overlayer on Ru nanoparticles has a stronger interaction with the O in diphenyl ether with preferential vertical adsorption, which inhibits the activation and hydrogenation of the aromatic ring, leading to higher selectivity for direct C–O bond cleavage. In the depolymerization of real lignin, the bimetallic Ru–MnO shows significantly higher (fivefold) activity than monometallic Ru under the tested condition. This work provides a general framework for the rational design of highly efficient catalysts for selective C–O bond cleavage.