Synergistic Ru-Co atomic pair with enhanced activity toward levulinic acid hydrogenation

Development of efficient metal-based catalysts is of great importance for levulinic acid (LA) hydrogenation to gamma-valerolactone (GVL). The widely employed Ru-based catalysts are advantageous for H2 dissociation, however, the steric hindrance of large Ru particles hampers their coordination to C--O moiety in LA, and thereby decreasing the activity. Herein, we report a Ru1Co1-N-C double single-atom catalyst (DSAC) with synergistic Ru and Co atomic pairs for LA hydrogenation into GVL. The Ru and Co doped zeolitic imidazole frameworks (RuCo-doped ZIF-8) precursor was rationally designed ((Ru + Co)/(Zn + Ru + Co) = 2 at.%), where the Zn node spatially isolates Ru and Co species, expanding the adjacent Ru-Co distance and facilitating the formation of the Ru-Co atomic pair upon pyrolysis, with each atom coordinated with three nitrogen atoms (N3-Ru1Co1-N3). The Ru1Co1-N-C catalyst exhibits outstanding catalytic activity, with a turnover frequency (TOF) of 1980 h-1, surpassing previously reported Ru-based catalysts. Experimental investigation and density functional theory (DFT) calculations reveal that the electron-rich Ru induced by less electronegative Co facilitates H2 dissociation, while atomic Ru in dual-atomic pairs promotes C--O activation, Ru and Co atomic pairs synergistically enhancing LA conversion to GVL. This research will shed light on the precise control of active sites at atomic scale, and also provides a new concept for designing high-performance Ru-based catalysts towards LA hydrogenation to GVL.