Reflux-synthesized bulk and diluted W-Nb-O mixed oxide bronzes for the valorization of short-chain oxygenates aqueous mixtures

Abstract

This work reports the preparation of bulk and KIT-6-diluted W-Nb-O mixed oxide bronzes by a reflux method. The influence of the incorporation of Nb and a mesoporous silica on the physicochemical features of the catalysts is studied. The addition of Nb favors the formation of single-phase oxide bronze structure, with improved Lewis acidity; while the incorporation of KIT-6 gives rise to well-dispersed mixed metal oxide particles on the diluter. These diluted W-Nb-O catalysts present enhanced surface areas and mesopore volumes. The materials have been tested in the valorization of an aqueous model mixture (acetol/propanal/ethanol/acetic acid/water weight ratio of 5/25/10/30/30), through C-C bond formation reactions. The increase in the Lewis nature of surface acid sites stands as the key point to maximize the total organic yield during the reaction (C 5 -C 10 products). The best catalysts maintain their catalytic behavior after five consecutive uses. The incorporation of Nb into the h -WO 3 framework by a reflux method leads to a loss of periodicity in the ab plane of the crystal structure, with a concomitant increase of surface Lewis acidity; thus giving rise to higher yields to C 5 -C 10 products in the valorization of aqueous model mixtures of short-chain oxygenates.