Molybdenum-containing systems based on natural kaolinite as catalysts for selective oxidation of aromatic sulfides

Abstract

A natural kaolinite from Argentinean deposits, converted into metakaolin by thermal treatment at 823 K and chemically modified, was used as a support for catalysts containing iso- and heteropolyanions (POMs and HPOMs) such as ammonium heptamolybdate (AHM) and ammonium Anderson phases [XMo6O24H6]3− [X(III) = Al, Co]. The catalytic performances were analyzed in the clean selective oxidation of diphenyl sulfide (DPS) with H2O2. The chemical modification included treatment in acid solution and functionalization with 3-(aminopropyl)trimethoxysilane (F). The characterization was carried out by X-ray powder diffraction (XRD), scanning electron microscopy (SEM) with energy dispersive spectrometry (EDS), FTIR and Raman spectroscopies. Textural properties were determined by N2 adsorption-desorption isotherms (BET method); surface acid properties (Brønsted and Lewis surface acid sites) were measured by FTIR of adsorbed pyridine. A noticeable increase of surface areas and chemical composition change of the support occurred by acid treatment. Functionalization with amino-siliceous agents yielded an appropriate surface for the adsorption of POMs and HPOMs. The system containing Mo presented conversions of diphenyl sulfide of around 90% and high selectivity to diphenyl sulfone near 95%.