Immobilization of ionic liquids in θ-zirconium phosphate for catalyzing the coupling of CO2 and epoxides

Abstract

The immobilization of 1-butyl-3-methylimidazolium chloride (BMIMCl) was achieved via the intercalation of BMIMCl into layered θ-zirconium phosphate (θ-ZrP), a hydrated form of α-zirconium phosphate. The intercalation process was studied by controlling the feed ratio of BMIMCl to θ-ZrP. X-ray diffraction characterization revealed that the formed intercalation compounds exhibited multiple phases depending on the intercalation ratio. θ-ZrP served as an excellent host for the intercalation of BMIMCl. The immobilized BMIMCl was evaluated via a coupling reaction of CO₂ and propylene oxide to synthesize propylene carbonate. The results showed that the immobilized BMIMCl could maintain a similar catalytic reactivity to un-supported BMIMCl. After immobilization, the BMIMCl catalyst could be effectively separated from the products and recycled, and the recycled catalyst maintained high reactivity. Overall, the immobilization of BMIMCl into θ-ZrP enables BMIMCl to be a “greener” catalyst for a green chemical process.