Covalent Triazine Frameworks as Heterogeneous Catalysts for the Synthesis of Cyclic and Linear Carbonates from Carbon Dioxide and Epoxides

The base catalytic properties of a series of triazine-based covalent organic frameworks were evaluated for the conversion of CO₂ to organic carbonates. The high number of basic nitrogen sites of the as-synthesized frameworks efficiently catalyzed the formation of cyclic carbonates via the cycloaddition of CO₂ to different starting epoxides. The structural and chemical tunability of the covalent triazine frameworks allowed the fine evaluation of key parameters influencing the observed catalytic activities. An increased surface area and presence of additional mesopores dramatically enhance the activity of the investigated catalytic materials. The chemical composition was also found to influence the reaction, as evidenced by an increased activity at lower reaction temperatures, when a more basic, pyridine-based, framework was used as catalyst. Finally, the activity in the two-step cycloaddition/transesterification catalysis of dimethyl carbonate was evaluated in a one-batch process.