V- and Nb-containing tungsten bronzes catalysts for the aerobic transformation of ethanol and glycerol. Bulk and supported materials

Abstract

[EN] This work report the applicability of reflux to the synthesis of supported tungsten bronzes (i.e. W-V-O and W-Nb-O), using mesoporous KIT-6 as inert support. For comparison, the corresponding bulk materials prepared by reflux or by hydrothermal synthesis have been also prepared. The catalysts were characterized by several techniques (X-ray diffraction, N-2 adsorption, temperature programmed desorption (NH3), and Raman and FTIR spectroscopies) and tested in the selective aerobic transformation of ethanol and glycerol. These results demonstrate the formation of V- and Nb-containing tungsten oxide bronzes in all of the heat-treated samples (bulk and supported materials), as well as the effective incorporation of metals (V or Nb) in the framework of tungsten bronzes. During the aerobic transformation of ethanol, diethyl ether and ethylene (in Nb-containing catalysts) and acetaldehyde, diethyl ether and ethylene (in V-containing catalysts) were the main reaction products, with very small formation of carbon oxides. During the aerobic transformation of glycerol, acrolein was mainly formed over Nb-containing catalysts, whereas acrylic acid, acrolein and COx were mainly observed over V-containing catalysts. The differences between bulk and supported catalysts have been explained according to changes in their physico-chemical properties: V-containing catalysts presenting both acid and redox sites; and Nb-containing catalysts presenting acid sites. In this way, supported materials seems to be effective in both redox and acid reactions due to the small modifications of the acid characteristics of catalysts.