Niobium-doped phosphomolybdic acid catalyst includedin silica matrix: study of stability and reactivity using different loads

Abstract

Heteropolyacids are used as catalysts in numerous reactions because they are inexpensive, nontoxic, have high acid strength and excellent redox proper-ties. They have been used as acid catalyst in different ways, and numerous studies indicate that the incorpo-ration of Nb into the structure of a solid generates an increase in the acidity of the sample, both at Lewis and Brönsted acid sites. Heteropolyacids have low surface area, which makes it necessary to include them in a support to increase the surface area and allow their use as heterogeneous catalysts in liquid phase reactions because they are very soluble in po-lar solvents. In this work, the synthesis of catalysts containing a niobium-doped heteropolyacid (PMoNb) included in silica at different concentrations is re-ported. The catalysts were characterized by ICP-MS, FT-IR, XRD, potentiometric titration, and their cata-lytic activity was tested in the selective oxidation of diphenyl sulfide to diphenyl sulfoxide, showing excel-lent results.