Niobia supported sulfated bismuth oxide nanorods (S-Bi2O3@Nb2O5): Acidic properties, catalytic activity and green metrics analysis

Abstract

A simple method was developed for the synthesis of sulfated bismuth oxide nanorods decorated with niobia (S-Bi2O3@Nb2O5). The material was well characterized with the help of several techniques such as FTIR, Raman, UV-vis DRS, PXRD, SEM/EDX, Elemental mapping, TEM, TGA, and BET analyses. Brønsted and Lewis acidic sites of the catalyst were measured using Hammett indicator method and pyridine FTIR spectroscopy respectively. The value of Hammett acidity function (H0 = 1.38) indicated the presence of significant number of Brønsted acidic sites while intense peak at 1452 cm−1 in the pyridine FTIR revealed the existence of a large number of Lewis acidic sites on the surface of material. Catalytic potential of the material was explored by synthesizing a library of pyrazolylmethanes via multicomponent reaction and results were excellent in terms of high product yield (90–98%) and reduced reaction time period (4–12 min). Solvent free reaction, ambient temperature, recyclability of the catalyst (up to five cycles), low E-factor (3.32–4.26), high atom economy (95.87–96.61%) and overall efficiency (92.04%–98.36%) confirmed the greenness of the present protocol.