Active form of 12-vanadomolybdophosphoric acids in n-butane selective oxidation

Abstract

The catalytic behaviour of H₅PV₂Mo₁₀O₄₀ heteropoly acid in the oxidation of n-butane to maleic anhydride is analysed in relation to that of its partially salified Cs salt and their FTIR spectra, UV–VIS diffuse reflectance spectra, thermogravimetry and reducibility tests as well as solid state ⁵¹V NMR and EPR characterizations are also compared. At temperatures around 573 K the acid sample dehydrates with partial reduction and the formation of lacunar oxo-anions but with preservation of the Keggin unit structure. The creation of inter-Keggin V—O—V bonds during dehydration is suggested. The presence of the alkali metal in the secondary structure inhibits these effects. The superior catalytic performance of the acid sample in butane transformation is discussed in terms of the role of the presence of V⁵⁺ sites associated with an inter-Keggin interaction.