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

Abstract

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 TeVO₄, Te₃Mo₂V₂O₁₇, Mo₄O₁₁ and TeO₂, which are very different from the crystalline phases of conventional Mo–V–Te–Nb-mixed metal oxides. While at lower temperatures, Mo₄O₁₁ 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 Mo₄O₁₁ and superficial Mo⁶⁺ and Te⁴⁺ ions are responsible for the high propylene conversion, while suitable acidic sites and superficial Nb⁵⁺ ions improved the selectivity to acrylic acid.