New niobium heteropolyacid included in a silica/alumina matrix: Application in selective sulfoxidation

Abstract

A new heteropolyacid, derived from phosphomolybdic acid containing niobium (PNbMo), was synthesized and included in silica, alumina, and silica/alumina matrixes by sol-gel technique, in order to use it as heterogeneous catalyst. The matrixes confer stability to the active phase, good textural and morphological properties. PNbMo and included materials were characterized by 31P-NMR, FT-IR, UV–vis, TGA, SEM, TEM, XRD, N2 physisorption, and potentiometric titration, and tested as catalyst in the sulfoxidation of diphenyl sulfide under suitable conditions. The redox activity was compared with phospomolybdic acid and correlated with the edge energy obtained from UV–vis absorption spectra. The best results in diphenyl sulfide sulfoxidation were obtained with PNbMo-SiAl-4:1 (92% conversion and 95% selectivity at 3 h) and with PNbMo-Si (92% conversion and 94% selectivity at 4 h). The reuse of these catalysts was evaluated.