Zn-MOF as a Single Catalyst with Dual Lewis Acidic and Basic Reaction Sites for CO<sub>2</sub> Fixation
Alehegn Eskemech, Hushan Chand, Anirban Karmakar, Venkata Krishnan, Rik Rani Koner
Abstract
Continuous increase in carbon dioxide (CO 2 ) emissions are causing imbalances in the environment, which impact biodiversity and human health. The conversion of CO 2 to cyclic carbonates by means of metal–organic frameworks (MOFs) as a heterogeneous catalyst is a prominent strategy for rectifying this imbalance. Herein, we have developed nitrogen-rich Zn (II) based metal–organic framework, [Zn(CPMT)(bipy)] n (CPMT = 1-(4-carboxyphenyl)-5-mercapto-1 H -tetrazole; bipy = 4,4′-bipyridine), synthesized via a mixed ligand strategy. This Zn-MOF showed high chemical stability in both acidic and basic conditions, and in organic solvents for a long time. On account of the concurrent presence of acid–base active sites and strong chemical stability under abrasive conditions, this Zn-MOF was employed as an effective catalyst for the coupling of CO 2 and epoxides, under atmospheric pressure, mild temperature, and neat conditions. This Zn-MOF shows remarkable activity by producing high yields of epichlorohydrin carbonate (98%) and styrene carbonate (82%) at atmospheric CO 2 pressure, 70 °C temperature, and 24 h reaction time, with turnover numbers (TON) of 217 and 181, respectively. The Zn-MOF could be reused for up to seven cycles with structural and framework integrity. Overall, this work demonstrates the synthesis of a novel and highly efficient MOF for CO 2 conversion.