Role of water in dual-ionic pyrazolium salt promoted conversion of CO2 at atmospheric pressure and room temperature

Abstract

Dual-ionic pyrazolium salts have in this work been synthesized and shown to catalyze the coupling reaction of carbon dioxide (CO₂) with epichlorohydrin achieving a 90% yield under 30 °C and 0.1 MPa CO₂ pressure. With the aid of a small amount of water, the product yield is greatly improved up to 99.5% under the same reaction conditions, which corresponds to a rate enhancement of up to 1.4 times for the formation of the carbonate. We propose and explore a dual origin of the role of water, first by affecting the gas to liquid mass transfer of CO₂, and second a mechanism where water triggers a proton transfer that in turn underlies efficient conversion of CO₂. This theoretically derived mechanism is also confirmed by ¹³C NMR and FT-IR spectroscopy results. The catalyst was found to be reusable eight times without obvious reduction of catalytic activity. The finding presented that an already efficient reaction to attract CO₂ is further greatly promoted only by the addition of water which can have important ramifications for green technology.