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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.

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Catalysts comprising Ru supported on CeO 2 with different morphologies have been widely investigated in various reactions, and the Ru/CeO 2 -nanorod catalysts have generally demonstrated higher performance. The strong interaction between Ru and CeO 2 nanorods, which is beneficial to oxygen activation, is usually considered to be responsible for the higher oxidation activity of the Ru/CeO 2 nanostructures. However, how the metal−support interaction of Ru/CeO 2 affects the activation of oxygen species still remains elusive. In this work, we prepared two nanostructures consisting of Ru supported on CeO 2 nanorod (NR) and nanocube (NC), and the Ru/CeO 2 -NR catalyst exhibited higher catalytic activity than Ru/CeO 2 -NC in the oxidation of formaldehyde (HCHO) and carbon monoxide (CO) at low temperatures. The results of complementary characterization techniques revealed that the interaction between Ru and CeO 2 -NC is actually stronger than that of Ru/CeO 2 -NR, and more interestingly, we observed that the different Ru−CeO 2 interactions induce distinct active oxygen species responsible for the oxidation reactions over Ru/CeO 2 -NR and Ru/CeO 2 -NC. The stronger interaction between Ru and CeO 2 -NC leads to the activation of lattice oxygen on CeO 2 -NC and a weakened redox capacity of RuO x species. In contrast, the moderate interaction between Ru and CeO 2 -NR induces a higher redox capacity of RuO x species but weak activation of lattice oxygen on CeO 2 -NR. The active RuO x on Ru/CeO 2 -NR is identified as being responsible for the high activity for HCHO/ CO oxidation, while the activated lattice O of CeO 2 -NC in the Ru−CeO 2 interfacial domain is the active species on Ru/CeO 2 -NC, rather than RuO x , resulting in low activity. These findings on Ru/CeO 2 nanostructures provide insight into understanding the metal−support interaction over Ru/CeO 2 catalysts.

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