Titania-heteropolyacid composites (TiO2-HPA) as catalyst for the green oxidation of trimethylphenol to 2,3,5-trimethyl-p-benzoquinone

PALACIO, MAGDALENA; VILLABRILLE, PAULA I.; PALERMO, VALERIA; ROMANELLI, GUSTAVO P.

JOURNAL OF SOL-GEL SCIENCE AND TECHNOLOGY

SPRINGER

Año: 2020

0928-0707

New catalysts containing phosphomolybdic acid (PMA) and vanadophosphomolybdic acid (VPMA) in a titania matrix were synthesized by the sol?gel process with different heteropolyacid loads (5%, 15%, and 30% (w/w): 5PMA-TiO 2 , 15PMA-TiO 2 30PMA-TiO 2 , 5VPMA-TiO 2 , 15VPMA-TiO 2 , and 30VPMA-TiO 2 ). The techniques used to characterize the materials were XRD, DRS, SEM, FT-IR, 31 P MAS-NMR, potentiometric titration with n-butylamine, and N 2 physisorption at −196°C. The materials were used as heterogeneous catalysts in the oxidation of 2,3,6 trimethylphenol (TMP) to 2,3,5-trimethyl-p-benzoquinone (TMBQ), a key intermediate in vitamin E synthesis. The catalysts allowed an ecofriendly TMBQ synthesis, using ethanol as solvent and aqueous hydrogen peroxide as a clean oxidizing agent, at room temperature. The conversion of TMP reached 90% and 99% for the samples with 15PMA-TiO 2 and 15VPMA-TiO 2 , respectively, after 4h. The amount of Mo and V in the reaction medium was determined by ICP-MS, which showed leaching of only 17?18% Mo, but 48% V. Reuse of the catalysts was performed. For 15PMA-TiO 2 , the conversion was maintained in the second cycle. A homolytic mechanism was proposed for TMBQ synthesis, which involved the formation of a peroxometallic species through an HPA-Ti center.