A solid solution zeolitic imidazolate framework as a room temperature efficient catalyst for the chemical fixation of CO2

Abstract

An energy efficient and economically viable bimetallic heterogeneous catalyst system composed of Co and Zn as active centers and 2-methylimidazole as a linker has been synthesized in water at room temperature. The synthesized material (CZ-ZIF) possesses a sodalite topology, similar to the parent materials, ZIF-8 and ZIF-67, with a high surface area of >1400 m² g⁻¹. The Zn and Co metal ions were shown to occupy equivalent sites throughout the framework in similar proportions, as confirmed by inductively coupled plasma atomic emission spectroscopy and energy dispersive X-ray spectroscopy techniques. CZ-ZIF rendered a high catalytic conversion of epoxides to five-membered cyclic carbonates using CO₂ as the C1 source under solvent- and co-catalyst-free conditions with excellent selectivity and manifested better catalytic abilities than ZIF-67 and enhanced framework stability compared to ZIF-8. Furthermore, CZ-ZIF exhibited catalytic activity even at room temperature in the presence of a co-catalyst, and was reusable over a minimum of five cycles with no noticeable decrease in activity. A plausible mechanism for CZ-ZIF catalyzed solvent- and co-catalyst-free epoxide–CO₂ cycloaddition has been proposed.