Nitrogen-rich covalent triazine frameworks as efficient supports for nickel-catalyzed CO2 conversion

A nitrogen-rich covalent triazine framework (CTF) with a low carbon-to-nitrogen (C/N) molar ratio of 1.46 was synthesized as a solid nitrogen-containing ligand, offering abundant coordination sites for the immobilization of nickel(II) acetate catalyst for CO2 utilization. The resulting heterogeneous Ni-CTF catalyst was thoroughly characterized by porosimetry, TGA, FTIR, Raman spectroscopy, SEM-EDAX, XPS, XRD, and CO₂ adsorption capacity analyses. Ni-CTF efficiently promoted the direct coupling of carbon dioxide with epoxides under relatively mild conditions (0.25 mol% Ni-CTF, 0.5 mol% TBAB, 7.5 bar CO₂, 100 °C). To clarify the individual roles of each catalytic component, a series of control experiments were conducted under identical conditions, including Ni-CTF alone, the pristine CTF, unsupported nickel(II) acetate, and various co-catalysts with distinct chemical properties. These systematic investigations provided deeper insight into the contributions to catalytic performance. Ni-CTF displayed excellent recyclability, retaining both activity and selectivity over at least four consecutive cycles without noticeable loss in performance. The observed catalytic performance is attributed to the organic nature of the CTF, which facilitates the diffusion of organic epoxide molecules, as well as to the nitrogen-rich functionalities embedded within the triazine network. These nitrogen sites, in conjunction with their ability to coordinate nickel species, significantly enhance the CO2 adsorption capacity of the catalyst.