Tungsten-vanadium mixed oxides for the oxidehydration of glycerol into acrilic acid

In this paper we report about the one-pot transformation of glycerol into acrylic acid, catalyzed by W/V mixed oxides. The reaction requires two different catalyst functions, i.e., an acid one, which is inferred by W oxide, and an oxidizing one, given by the V ions incorporated inside the WO3 lattice. W bronze is very active and moderately selective in acrolein formation, but yields only traces of acrylic acid. The incorporation of increasing amounts of V inside the hexagonal tungsten bronze structure, with development of a monophasic compound, allows the consecutive oxidation of acrolein into acrylic acid. An optimal atomic ratio between W and V equal to V/(W+V)=0.3 allowed obtaining an acrylic acid yield of 26% (with selectivity to residual acrolein of 11%). However, during reaction under the oxygen-containing feed, the V4+ incorporated in the hexagonal bronze structure underwent a slow oxidation into V5+, which caused a progressive decline of selectivity to acrylic acid and a concomitant increase of COx formation; the hexagonal structure however to be stable during lifetime experiments. On the other hand, in the absence of oxygen a very rapid deactivation of the catalyst occurred, with decrease of selectivity to acrolein and increase of heavy by-products.