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

Article abstract of DOI:10.1016/j.cattod.2012.06.004

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 WO ₃/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 (Nb₈W₉O ₄₇) and the acid-treated Cs_0.5[Nb_2.5W _2.5O₁₄] 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 Cs_0.5[Nb_2.5W_2.5O₁₄]. The results suggest that the structure of a-b plane affects the product distribution.