Design of Fe-modified mesoporous nanostructures as efficient catalysts for microwave-assisted selective oxidations of sulfides

Abstract

Redox catalysts modified with Fe were synthesized via wet impregnation of metal species loaded on SBA-15. The influence of a number of Fe precursors with distinctive counter-ions on the deposited metal species was studied. Materials were characterized by XRD, N2 physisorption, TEM, UV–vis DR, TPR and adsorption-desorption of pyridine followed by FT-IR. The redox properties were determined in the oxidation of diphenyl sulfide assisted by microwave irradiation. The reaction was carried out in ethanol as solvent and using Urea-H2O2 as oxidant, both chosen for their greener properties. Conversion and selectivity to diphenyl sulfoxide were found to be optimum when iron chlorides were employed as metal precursors in the synthesis. These iron sources led to the formation of nanoclusters in the surface, resulting in more available and exposed iron oxide sites and, in consequence, an enhanced oxidation potential and improved catalytic performance. Finally, these solids were reused after 4 reaction cycles without loss of their activity, corroborating in this way, the high stability of Fe species loaded into the silicate matrix.