Strategic design and facile synthesis of porous hyper-cross-linked phosphonium bromide microspheres for catalyzing CO2 conversion to cyclic carbonates

Abstract

Heterogeneous ionic liquid (IL) catalysts with multiple active sites can be considered as the highly efficient catalyst for CO2 conversion to cyclic carbonates. It is extremely challenging to achieve the strategic design and precise control of multi-site polymeric ILs’ morphology and properties. In this work, we developed a novel and facile polymerization-ionization method employing flexible brominated monomers as raw materials (e.g. 4‑bromo-1-butene) to successfully synthesize porous hyper-cross-linked phosphonium bromide-microspheres (PBr-microspheres), in order to break through the drawbacks of multi-step preparation and difficulty in microsphere forming. Compared with conventional bromine spheres of the same size, the specific surface area of the new synthetic bromine sphere is 16 times, and the average pore size is one-eighth, with 3-times CO2 adsorption capacity, with rich microporous structure and exposed active sites, excellent CO2 adsorption capacity and thermal stability. PBr-microspheres can achieve synergistic effect of physical adsorption and chemical interaction for CO2, thus enhancing the catalytic performance in CO2 conversion process, affording propylene oxide conversion of 99.7 % and propylene carbonate selectivity of 99.9 %, while the catalytic activity did not decrease significantly after reusing 8 runs. This facile controllable synthesis of PBr-microspheres with excellent catalytic performance provides a new idea for heterogeneous ILs-catalyzed CO2 utilization.