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.