Basicity controlled MgCo2O4 nanostructures as catalyst for viable fixation of CO2 into epoxides at atmospheric pressure

Abstract

The present work demonstrates basicity controlled MgCo2O4 spinel oxides as promising catalysts for fixation of CO2 into epoxides at atmospheric pressure. Four different MgCo2O4 nanostructures were synthesized using different interlayer anions (chloride, nitrate, acetate, sulphate) present in the metal salt precursors which strongly altered their basicity and played a stimulating role in their catalytic efficiency. The characterization results of all four MgCo2O4 nanostructures revealed effect on morphology, surface area and developed diversely exposed Lewis basic (O2−) sites on the catalyst surface. Particularly, [MgCo2O4]-[Cl−] nanostructures prepared using chloride (Cl−) anion showed porous 3D-flower morphology with high pore diameter and highly exposed basic sites. Catalytic activity studies revealed that [MgCo2O4]-[Cl−] catalyst in presence of base, exhibited 95% conversion of styrene oxide and 96% selectivity towards styrene carbonate at atmospheric pressure. The enhanced activity of [MgCo2O4]-[Cl−] was due to the relatively smaller size of Cl− anion which replaced the hydroxyl groups in the Brucite-like structure and exposed maximum number of basic (O2−) sites during the thermal decomposition of the Mg-Co DH-[Cl−] precursor. Additionally, various reaction parameters were investigated to optimize reaction conditions. The obtained results with [MgCo2O4]-[Cl−] and base suggested that this catalytic system showed good tolerance for a broad substrate scope in good yields and demonstrated good reusability with retention in activity and physicochemical properties for eight recycles. A plausible mechanism was proposed to support the activation of epoxide and CO2 by the unique cooperation of active Lewis acidic and basic sites present in [MgCo2O4]-[Cl−] for formation of cyclic carbonates at atmospheric pressure.