Water-Modulated Ru Catalysis: Overcoming the Activity-Selectivity Trade-Off in C-O Bond Cleavage

Selective catalytic C-O bond hydrogenolysis is a promising approach to valorize lignin and its oligomer derivatives; however, most of the developed catalyst systems are still confronted with the issue of an activity-selectivity trade-off. In this work, we report water modulation to Ru-based catalysis in the hydrogenolysis of diphenyl ether, a model compound for the strongest C-O linkage in lignin and its derived oligomer. The combination of complementary characterizations and kinetic studies along with the density functional theory (DFT) calculation demonstrates that Ru supported on carbon nanotubes (Ru/CNT) can be stabilized in an oxidized state by water, which has a much less intensive interaction with and thus activation to the aromatic ring to inhibit deep hydrogenation. Moreover, the presence of water on Ru species also reduced the reaction barrier of C-O bond cleavage, leading to significantly promoted hydrogenolysis activity. Consequently, the activity-selectivity trade-off was overcome in Ru catalysis by water modulation. The similar effect of water to enhance both the activity and selectivity was also observed in the Ru supported on activated carbon (AC) and titanium dioxide (TiO₂) systems. This work provides a facile and efficient approach to achieve both highly active and selective C-O bond cleavage.