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

• W–V–Nb–O complex metal oxides having a structure like that of orthorhombic Mo3VOx were synthesized by hydrothermal method.
• The materials were an efficient catalyst for the gas-phase direct oxidative transformation of glycerol to acrylic acid.
• The catalytic performance was further improved by the surface modification with phosphoric acid, achieving ca. 60% one path yield of acrylic acid.

W–V–Nb–O 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–O catalyst without V component, mainly promoted the glycerol dehydration, giving acrolein selectively. Since Nb–O catalyst showed poor activity for the reaction, the introduction of W into the Nb–O catalysts was found effective for improving the activity for the dehydration of glycerol to acrolein. This is mainly due to the increase of Brönsted acidity by the combination of W and Nb. When V was incorporated into the framework of W–Nb–O, the resulting catalyst was found to prominently promote the formation of acrylic acid in the glycerol transformation in the presence of O2, 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.

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