Single Sodium Atoms on Polymer-Derived N-Doped Carbon as an Efficient Solid Strong-Base Catalyst for Transesterification

Solid base catalysts have found extensive applications in a variety of catalytic reactions because of their notable properties, including a high concentration of basic sites, straightforward recoverability, and favorable environmental compatibility. Nevertheless, these materials are susceptible to the agglomeration of basic sites, as well as the leaching of active components in the catalytic processes. In the domain of solid base catalysis, simultaneously achieving high dispersion and stability of active sites remains a consequential challenge. Herein, a sodium single-atom solid base catalyst was synthesized successfully by employing an impregnation-pyrolysis methodology. Isolated sodium single atoms were immobilized onto a polymer [synthesized from the polymerization of 2,4,6-tris(bromomethyl)mesitylene and 3,5-diamino-1,2,4-triazole] derived nitrogen-doped carbon (PDNC) framework, resulting in the successful fabrication of Na1/PDNC. Experimental characterizations and theoretical simulations prove that the sodium single atoms are stabilized among the support matrix in a penta-coordinated geometry, specifically as Na–C3N2 moieties. The exceptional catalytic performance and structural robustness of the material originate from the effective anchoring of atomically dispersed sodium species by nitrogen dopants, which stabilize the active sites and prevent their aggregation. The obtained catalyst was employed for the synthesis of dimethyl carbonate (DMC) by means of transesterification reaction between ethylene carbonate (EC) and methanol. Moreover, the Na1/PDNC exhibited a DMC yield of 50.6% and the turnover frequency (TOF) reached 114.9 h–1. These results significantly exceed those obtained with the comparative catalyst Na2O/PDNC (TOF = 32.6 h–1) as well as the basic catalysts reported before. Furthermore, the Na1/PDNC catalyst demonstrated high stability, maintaining consistent activity over four successive cycles without a pronounced loss in catalytic performance.