Vanadium in cationic and anionic positions as a promoter of 12‐molybdophosphoric‐acid‐based catalysts

Abstract

Derivatives of 12‐molybdophosphoric acid (H3PMo12O40), containing vanadium in the form of a vanadyl cation or substituted as addenda in Keggin anions, have been synthesized and characterized by IR, LRS, XPS, NMR, and DTA/DTG. Their catalytic behavior in the oxidation of methanol, butane and pentane has been determined. Both catalysts exhibit strong acidity, due to hydrolysis of the secondary structure in the case of the salt. The vanadium atom performs its role as the active site for the activation of hydrocarbon molecules irrespective of whether it is present as a cation or incorporated in Keggin anions.

Catalysis by heteropoly compounds Part 39 The structure and redox behaviour of vanadium species in molybdovanadophosphoric acid catalysts during partial oxidation of isobutane

“…The pre-treated catalysts were transferred from the reactor tube into a mixed solvent of 1,4-dioxane and water (7 : 3, v/v) in an Ar-Ðlled bag to avoid absorption of moisture prior to the dissolution. The concentrations of catalysts were adjusted to 16…”

Optical bands of dodecanuclear compounds H4PVMo11O40·yH2O with Keggin structure. Semiclassical vibronic model

“…located inside the primary (oxoanion) and/or the secondary structure. 16,30,31 In the Keggin polyanion the octahedra VO 6 and MoO 6 can share a corner or an edge. Much less is known about the oxygen surrounding of V and the junction of Mo and V ions when V is located in the secondary structure.…”

“…(32) into eqn. (31) and proceed with the calculation of the integrals S ij that appear in the transfer parameters p i . The integrals S ij in eqn.…”

“…The integrals S ij in eqn. (31) account for the overlap between the dfunctions of neighboring metal sites, the overlap between the d-functions and the p p ligand functions as well as the overlap between the p p functions of ligands surrounding different metal sites. The schematic illustration of the overlap of the d and p p orbitals in the case of metal sites sharing a corner or an edge is shown in Fig.…”

“…In the real Keggin molecule the M-O-M angles are equal to 150 and 121 for neighboring metal sites linked through a corner or an edge, respectively. 51 While calculating the values S ij (31) the C.E. Scha ¨ffer's tables 45 which give the form of the d-function of a metal ion in the coordinate system of another metal site or in the coordinate system of a ligand were employed.…”