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.