Nitrogen-rich metal–organic framework of nickel(ii) as a highly efficient and reusable catalyst for the synthesis of cyclic carbonates at ambient pressure of CO2†

Abstract

Nitrogen-rich metal organic frameworks (MOFs) structures have a great potential for the chemical fixation of CO₂. In this direction, we have utilized the highly efficient nitrogen-rich dual linker MOF of nickel(II) as a heterogeneous catalyst in solvent-free chemical fixation of CO₂ into cyclic carbonates at ambient pressure. In this present work, nitrogen-rich nickel-MOF, Ni-ImzAdn, was synthesized from imidazole and adenine as efficient nitrogen-rich linkers under hydrothermal conditions (Imz = Imidazole and Adn = Adenine). The Ni-ImzAdn was characterized thoroughly via various physicochemical analyses such as FT-IR, SEM, EDX, EDX-mapping, XRD, ICP-OES, BET, BJH, TG-DTA, CO₂-TPD, and NH₃-TPD. Ni-ImzAdn with adequate free nitrogen sites exhibit high catalytic activity in the cycloaddition of CO₂ with styrene oxide (93% yield) at solvent-free and ambient pressure. The high activity of Ni–ImzAdn was attributed to the synergistic effect of strong Lewis acid and strong Lewis base sites on the catalyst, which were acquired by CO₂ and NH₃-TPD respectively. In addition, the MOF catalyst was presented as highly recyclable without significant loss of activity after six reaction cycles and low metal ion leaching (analyzed by (ICP-OES)). Thermogravimetry-differential thermal analysis (TG-DTA) showed the MOF catalyst had high thermal stability up to 318 °C.