Facile fabrication of a heterogeneous Co-modified pyridinecarboxaldehyde-polyethylenimine catalyst for efficient CO₂ conversion under mild conditions

A heterogeneous Co-modified pyridinecarboxaldehyde-polyethylenimine catalyst (Co-Py-PEI) with highly active metal sites and amine groups was facilely prepared and thoroughly characterized. The novel Co-Py-PEI catalyst together with Bu₄NBr exhibited efficient catalytic properties for the conversion of CO₂ into cyclic carbonates under the mild conditions of 80 °C, 1.0 MPa and 5 h, and 99% yield of propylene carbonate was obtained even in combination with 7.2 mol% Bu₄NBr loading under the conditions of room temperature, 1.0 MPa and 24 h. The high activity for CO₂ cycloaddition reaction to generate cyclic carbonate was ascribed to the synergistic catalysis of Lewis acid-base sites and bromide ions in the Co-Py-PEI/Bu₄NBr catalyst system. Moreover, the Co-Py-PEI catalyst exhibited outstanding thermal and structural stability, besides its simple recovery by centrifugation and its excellent recyclability of up to seven runs. Thus, the Co-Py-PEI catalyst is considered to be a satisfactory candidate for the coupling reaction of CO₂ and epoxides.