Calcium single atom catalyst with unusual activity and stability for the synthesis of dimethyl carbonate.

Solid base catalysts with strong basicity are highly desirable for various reactions because of their minimal corrosion, ease of separation, and environmental sustainability. Nevertheless, their broader application is hindered by issues including mediocre activity and poor stability. Herein, aiming at enhancing the catalytic performance and stability of conventional solid bases, we designed and fabricated calcium (Ca) single-atom solid bases on zeolite imidazolate framework (ZIF-8) derived N-doped carbon (NPC) with Ca-N4 motifs as the active center for transesterification of methanol and ethylene carbonate. Benefiting from the highly dispersed Ca atoms and strong metal-substrate interaction, the Ca1/NPC exhibits unusual activity (35.1 %) and stability (5 cycles without obvious deactivation) in transesterification to produce dimethyl carbonate (DMC), which significantly surpasses its analogue CaO/NPC and multiple reported alkali/alkaline-earth metal derived solid base catalysts with superbasicity. Moreover, the turnover frequency (TOF) is 123.0 h-1 on Ca1/NPC, significantly surpassing that of traditional Ca-based counterparts (6.4 and 8.6 h-1) and even outperforming typical alkali metal derived catalysts with superbasicity (6.8-36.2 h-1). This study not only offers an advanced Ca-N-based catalyst for transesterification but also provides direction for fabricating single-atom solid strong bases for a variety of heterogeneous catalytic process.