Nitrogen-rich dual linker MOF catalyst for room temperature fixation of CO2 via cyclic carbonate synthesis: DFT assisted mechanistic study

Abstract

The benign synthesis of a novel Zn based Lewis acid-base bifunctional metal-organic framework (ITH-1) and its room temperature catalytic ability for the chemical fixation of carbon dioxide via cyclic carbonate synthesis is reported herein. ITH-1 is characterized by the presence of mono coordinated pendant imidazole groups throughout the framework inducing Lewis basicity. The synthesized material is crystallized in the monoclinic space group as revealed by the Single Crystal X-ray Diffraction Analysis and possesses a 2 D non-planar interdigitated network wherein the neighbouring sheets are connected via strong hydrogen bonding (1.947 Å). ITH-1 was characterized thoroughly via various physicochemical analyses such as XRD, FT-IR, Raman, FE-SEM, CHN, ICP, TGA and was found thermally stable up to 300 ⁰C. The co-existence of accessible and active Lewis acid (Zn) –Lewis base (imidazole) moieties rendered ITH-1 the potential to catalyse the cycloaddition of CO2 with propylene oxide under solvent and co-catalyst free conditions (~95% conversion) at moderate temperatures with remarkable reusable performance (over 5 times). ITH-1 manifested excellent CO2 conversion even under room temperature and 1 bar pressure in the presence of a co-catalyst. Density Functional Theory (DFT) calculations utilizing M06 functional were exercised to envisage the mechanism behind the successful CO2 conversion by ITH-1 at room temperature and were found to be in clear agreement with the experimental results.