Facile sub-/supercritical water synthesis of nanoflake MoVTeNbO x -mixed metal oxides without post-heat treatment and their catalytic performance.

A fast and simple sub-/supercritical water synthesis method is presented in this work in which MoVTeNbO x -mixed metal oxides with various phase compositions and morphologies could be synthesized without post-heat treatment. It was demonstrated that the system temperature for synthesis had a significant influence on the physico-chemical properties of MoVTeNbO x . Higher temperatures were beneficial for the formation of a mixed crystalline phase containing TeVO 4 , Te 3 Mo 2 V 2 O 17 , Mo 4 O 11 and TeO 2 , which are very different from the crystalline phases of conventional Mo-V-Te-Nb-mixed metal oxides. While at lower temperatures, Mo 4 O 11 was replaced by Te. At high temperature, the as-prepared samples presented distinct nanoflake morphologies with an average size of 10-60 nm in width and exhibited excellent catalytic performances in the selective oxidation of propylene to acrylic acid. It is illustrated that the large specific surface area, presence of Mo 4 O 11 and superficial Mo 6+ and Te 4+ ions are responsible for the high propylene conversion, while suitable acidic sites and superficial Nb 5+ ions improved the selectivity to acrylic acid.