Synergistic interaction of anions and cations in preparation of VPO catalysts promoted by polyoxometalate-ionic liquids

Abstract

Vanadyl pyrophosphate (VPO) catalyst exhibits a unique ability to activate CH bond and selectively oxidize n-butane to maleic anhydride (MA). Here, a novel “function-oriented design” strategy was proposed to design and develop single-component additive polyoxometalate-ionic liquids (POM-ILs) with dual-function to enhance the activity of VPO catalyst. And the synergistic interaction of anions and cations of POM-ILs was illuminated combined with characterizations. The IL-cations guide the growth of the catalyst precursor to ordered nanolamellar structure rather than three-dimensional disordered rose-like. Correspondingly, it makes the catalyst exhibit a unique mesh-hole structure and benefit exposure of the active surface (200) of (VO)2P2O7. The POM-anions decompose into the defective OPMo compound and cause more oxygen vacancies and crystal defects formed on the surface of VPO after activation. Besides, we established a specific method to divide the poly-acids (α, β, γ-acid) sites to describe the acidic properties on the surface of VPO by NH3-TPD in qualitatively and quantitatively and related with catalytic performance.