Nanostructured functionalised niobium oxide as chemoselective catalyst for acetalation of glucose

Developing a chemoselective catalyst for the acetalation of biomass-derived glucose to alkyl glycosides has been recognised as an emerging field due to its wide range of applications. The present study focuses on synthesising sulfate functionalised niobium oxide-based (NbOx-DS) catalyst to introduce medium/strong acidic sites that contribute to the catalytic activity towards glucose acetalation, which has not been explored previously. The nanosized NbOx-D is prepared via a precipitation approach using niobium chloride and diethylamine as a precursor and precipitating agent, respectively. The sulfate groups incorporated NbOx-DS gives a good yield of ethyl glucosides (60%) with excellent selectivity (97%) in ethanol. On the other hand, the sulfate groups incorporated into the commercial niobium oxide (NbOx-CS) exhibits poor catalytic activity, yielding 6% ethyl glucoside with a low selectivity (8%). FTIR analysis corroborates the incorporation of sulfate groups in the NbOx-DS matrix, unlike NbOx-CS. XRD pattern of NbOx-DS shows a lower angle shift of a peak to 23.5° compared to parent NbOx-D (24.32°), indicating lattice expansion due to the incorporation of sulfate groups, and no such a shift in the case of NbOx-CS is observed. NH3- temperature programmed desorption ( NH3-TPD) reveals that NbOx-DS possess a 2.1-fold higher number of acidic sites than NbOx-D, whereas NbOx-CS possess a negligible number of acidic sites, indicating the significance of the synthesis procedure of NbOx-D for efficient incorporation of sulfate groups. NbOx-DS displays recyclability for at least three runs with minor loss in the activity. In a nutshell, the current study reflects that NbOx-DS obtained via precipitation followed by sulfate groups incorporation increases the medium/strong acidic sites, which contributes significantly to enhancing the ethyl glucoside selectivity (97%).