Hydrothermal synthesis of W–Nb complex metal oxides and their application to catalytic dehydration of glycerol to acrolein

W–Nb complex metal oxides (W–Nb–O) having a layered structure (linear arrangement of corner-shared octahedra) in the c-direction and a disordered structure in the a–b plane were prepared by a hydrothermal synthesis method. Following calcination of W–Nb–O at a temperature below 973 K resulted in a high yield of acrolein of more than 70% in gas-phase glycerol dehydration in the presence of water and oxygen. The acrolein yield and the deactivation rate in the W–Nb–O was found to be higher and slower respectively than those of WO3/ZrO2 and H-ZSM-5 which are typical acid catalysts. Product selectivity over W–Nb complex metal oxides, which have the same layered structure in the c-axis direction were tested at comparable glycerol conversion rates. The tetragonal W–Nb–O catalyst (Nb8W9O47) and the acid-treated Cs0.5[Nb2.5W2.5O14] having orthorhombic structure showed different selectivity for glycerol transformation. However, the hydrothermally synthesized W–Nb–O calcined at a lower temperature had comparable acrolein selectivity to acid-treated Cs0.5[Nb2.5W2.5O14]. The results suggest that the structure of a–b plane affects the product distribution.