Porous polymeric hollow fibers as bifunctional catalysts for CO2 conversion to cyclic carbonates

- The highly solvent-stable and porous Br/APS-grafted ZrO2-PAI hollow fiber were prepared.
- Styrene carbonates were synthesized from styrene oxide with CO2 using cooperative Br/APS/Zr-PAI-HF catalyst.
- Porous ZrO2-PAIHF provides a physical barrier to prevent cooperative Lewis acid/base species and nucleophilic parts leaching.
- A plausible mechanism for cycloaddition reaction over bifunctional Br/APS/Zr-PAI-HF catalyst was proposed.

In this study, development of cooperative catalyst is demonstrated whereby Lewis acid/base species and nucleophilic parts are immobilized in the pores of a polyamide-imide (PAI) hollow fiber support. The highly solvent-stable and porous Br/APS-grafted ZrO2-PAI hollow fiber (Br/APS/Zr-PAIHF) catalyst was created by crosslinking of bare ZrO2-PAIHF polymer with 3-aminopropyltrimethoxysilane (APS) followed by alkylation with 1,2-dibromoethane at 110 °C. This bifunctional catalyst consists of a porous ZrO2-PAIHF polymer crosslinked with APS that was further immobilized with nucleophilic bromide ions. Porous ZrO2-PAIHF provides a physical barrier to prevent cooperative Lewis acid/base species and nucleophilic parts movement, aggregation, and detachment from the support into the product stream. The performance of Br/APS/Zr-PAIHFs as heterogeneous catalyst was investigated for the reaction of carbon dioxide (CO2) with styrene oxide (SO) which leads to the formation of styrene carbonate (SC). The influence of various reaction parameters including reaction temperature, reaction time, solvents, and CO2 pressure were systematically investigated in detail. Our results indicated that the synergistic cooperative effect of nucleophilic bromide ion (Br−) and Lewis acid/base species on PAIHF supports leads to a maximum SC selectivity of 99.1%. Additionally, SO conversion of 100% and excellent SC selectivity of 98% were obtained over Br/APS/Zr-PAI-HF catalyst.

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