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

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.