Single Sodium Atoms Anchored on N-Doped Porous Carbon: Solid Strongly Basic Catalysts with Uncommon Activity and Stability

Solid strong base catalysts have high potentials in a variety of reactions due to the advantages of negligible corrosion, easy separation, and high efficiency. However, two issues hinder the applications of such catalysts seriously, namely aggregation of basic sites and leaching of active species during reactions. The development of solid strong base catalysts with active sites that are highly dispersed and stable remains a pronounced challenge. In this work, we employed a two-step reduction strategy to anchor Na single atoms on nitrogen-doped porous carbon (NPC) support, producing a high-performance solid strongly basic catalyst named as Na₁/NPC. The alkali precursor NaNO₃ was converted to Na₂O on NPC at 400 ^oC, in which conventional solid base catalyst Na₂O/NPC was generated. Upon heat treatment at 850 ^oC, Na₂O was further reduced to Na single atoms anchored on NPC, creating Na₁/NPC. Experimental studies and theoretical calculations show that Na is structurally embedded on the support in penta-coordinated configuration (Na-C₃N₂). The synergistic effect of highly dispersed Na atoms and nitrogen doping results in uncommon catalytic activity and stability. In transesterification between methanol and ethylene carbonate to produce dimethyl carbonate (DMC), the yield of DMC reaches 48.4% over Na₁/NPC, corresponding to a turnover frequency (TOF) of 129.4 h^-1, which is far beyond the conventional counterpart Na₂O/NPC (63.3 h^-1) and various reported solid base catalysts. The catalytic activity of Na₁/NPC almost keeps constant during five cycles, while 87% of activity is lost for Na₂O/NPC due to the leaching of basic sites. This work might offer new ideas for the development of efficient single-atom solid strong base catalysts with high efficiency.