Synergistic RuCo 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 γ-valerolactone (GVL). The widely employed Ru-based catalysts are advantageous for H dissociation, however, the steric hindrance of large Ru particles hampers their coordination to CO moiety in LA, and thereby decreasing the activity. Herein, we report a RuCoNC 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 RuCo distance and facilitating the formation of the RuCo atomic pair upon pyrolysis, with each atom coordinated with three nitrogen atoms (NRuCoN). The RuCoNC catalyst exhibits outstanding catalytic activity, with a turnover frequency (TOF) of 1980 h, 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 H dissociation, while atomic Ru in dual-atomic pairs promotes CO 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.