Direct oxidative transformation of glycerol to acrylic acid over Nb-based complex metal oxide catalysts

W-V-Nb-0 complex metal oxides having a structure like that of orthorhombic Mo3VOx, were found to be an efficient catalyst for the gas-phase direct oxidative transformation of glycerol to acrylic acid. The catalysts with various compositions were facilely synthesized by hydrothermal method. The W-Nb-0 catalyst without V component, mainly promoted the glycerol dehydration, giving acrolein selectively. Since Nb-0 catalyst showed poor activity for the reaction, the introduction of W into the Nb-0 catalysts was found effective for improving the activity for the dehydration of glycerol to acrolein. This is mainly due to the increase of Bronsted acidity by the combination of W and Nb. When V was incorporated into the framework of W-Nb-0, the resulting catalyst was found to prominently promote the formation of acrylic acid in the glycerol transformation in the presence of O-2, while showed no effect on the dehydration of glycerol to acrolein. It was also found that V acts as an oxidation site only when glycerol is completely reacted. The optimum elemental composition for the reaction was W2.2V0.4Nb2.4O14 giving ca. 46% one path yield of acrylic acid and this catalytic performance was further improved by the surface modification with phosphoric acid, achieving ca. 60% one path yield of acrylic acid. (C)2015 Elsevier B.V. All rights reserved.