A copper-functionalized zirconium metal–organic framework for catalytic oxidative carboxylation of olefins and CO2

Abstract

Selective CO₂ adsorption and catalysis conversion of CO₂ to high value-added chemicals not only gives an effective way to reduce the concentration of CO₂ but also provides the precursors for industrial manufacturing of chemicals and fuels. With well-defined frameworks, flexible modifiability, and permanent porosity, metal–organic frameworks (MOFs) can be the ideal platforms for CO₂ utilization applications. In this work, a copper functionalized-zirconium MOF, denoted Zr-CPB-Cu (CPB = 1,2,3,4,5,6-hexakis(4-carboxyphenyl)-benzene), was successfully produced via post-metalation of copper(II) ions into a presynthesized Zr-CPB MOF. The bimetallic Zr-CPB-Cu containing two open metal sites (Zr⁴⁺ and Cu²⁺), polarized groups (e.g., uncoordinated –COOH, monodentate carboxylates, and acetate anions), accessible triangular channels, and permanent porosity (S_BET = 420 m² g⁻¹) revealed outstanding selective CO₂ adsorption and catalytic activity for the oxidative carboxylation of CO₂ and olefins. As a proof of concept, the Zr-CPB-Cu showed higher low-pressure capacities of CO₂, CH₄, and N₂ at room temperature and larger CO₂ selectivities over N₂ and CH₄ than those of the parent Zr-CPB. As for catalysis of CO₂ conversion, the Zr-CPB-Cu catalyst exhibited exceptional performance in direct synthesis of styrene carbonate from styrene and CO₂ with 97% conversion of styrene, and 92% yield of styrene carbonate in the presence of anhydrous TBHP oxidant and under mild conditions (1 atm of CO₂, 80 °C, and 12 h). Notably, the catalytic activity of Zr-CPB-Cu outperformed that of the parent Zr-CPB and other MOFs, and the recovered Zr-CPB-Cu can be reused up to six times without considerable reduction in catalytic activity. Our result envisaged an effective approach for the elaboration of MOFs as efficient heterogeneous catalysts for CO₂ separation and catalytic conversion of CO₂.