Preparation of polyvinyl alcohol–chitosan–NH4Br catalyst and its application to cycloaddition of carbon dioxide to propylene oxide

Abstract

An eco-friendly polyvinyl alcohol (PVA)–chitosan(CS)–NH4Br catalyst was prepared using a modified solution method. Although the amounts of PVA and CS were fixed, the amount of NH4Br was varied in the range 15–45 wt.%. The catalytic performance of PVA–CS–NH4Br was compared based on the carbonation performance in the presence of single-component catalysts (PVA, CS, and NH4Br) and dual component catalyst (PVA–CS). The catalytic activity of PVA–CS was inadequate and considerably less than that observed when either PVA or CS was exclusively loaded. The number of functional groups within the PVA–CS structure was presumed to have been reduced due to the interactions of the OH groups in PVA and CS. However, the PVA–CS–NH4Br catalyst distinctively exhibited its catalytic performance. It has been suggested that NH4Br aided in sustaining the innate functional groups that both PVA and CS have within the PVA–CS–NH4Br structure. These results indicate that the functional groups and nucleophiles within the PVA–CS–NH4Br structure more effectively participated in the carbonation of propylene oxide. Quantitatively, the addition of 30 wt.% NH4Br yielded the best performance. Characteristic analyses of the catalysts were performed using X-ray diffraction, thermogravimetric analysis, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy.