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In 1906, the preparation of “molybdic acid hydrate” was published by Arthur Rosenheim. Over the past 40 years, a multitude of isostructural compounds, which exist within a wide phase range of the system MoO3−NH3−H2O, have been published. The reported molecular formulas of “hexagonal molybdenum oxide” varied from MoO3 to MoO3·0.33NH3 to MoO3·nH2O (0.09 ≤ n ≤ 0.69) to MoO3·mNH3·nH2O (0.09 ≤ m ≤ 0.20; 0.18 ≤ n ≤ 0.60). Samples, prepared by the acidification route were investigated using thermal analysis coupled online to a mass spectrometer for evolved gas analysis, X-ray powder diffraction, Fourier transform infrared, Raman, magic-angle-spinning 1H- and 15N NMR spectroscopy, and incoherent inelastic neutron scattering. A comprehensive characterization of these samples will lead to a better understanding of their structure and physical properties as well as uncover the underlying relationship between the various compositions. The synthesized polymeric parent samples can be represented by the structural formula (NH4)(x∞)(3)[Mo(y square 1−y)O(3y)(OH)(x)(H2O)(m−n)]·nH2O with 0.10 ≤ x ≤ 0.14, 0.84 ≤ y ≤ 0.88, and m + n ≥ 3 − x − 3y. The X-ray study of a selected monocrystal confirmed the presence of the well-known 3D framework of edge- and corner-sharing MoO6 octahedra. The colorless monocrystal crystallizes in the hexagonal system with space group P6(3)/m, Z = 6, and unit cell parameters of a = 10.527(1) Å, c = 3.7245(7) Å, V = 357.44(8) Å3, and ρ = 3.73 g·cm(−3). The structure of the prepared monocrystal can best be described by the structural formula (NH4)(0.13∞)(3)[Mo(0.86 square 0.14)O2.58(OH)0.13(H2O)(0.29−n)]·nH2O, which is consistent with the existence of one vacancy (square) for six molybdenum sites. The sample MoO3·0.326NH3·0.343H2O, prepared by the ammoniation of a partially dehydrated MoO3·0.170NH3·0.153H2O with dry gaseous ammonia, accommodates NH3 in the hexagonal tunnels, in addition to [NH4]+ cations and H2O. The “chimie douce” reaction of MoO3·0.155NH3·0.440H2O with a 1:1 mixture of NO/NO2 at 100 °C resulted in the synthesis of MoO3·0.539H2O. This material is of great interest as a host of various molecules and cations.

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We present the V L3 near edge X-ray absorption fine structure (NEXAFS) of a vanadium phosphorus oxide (VPO) catalyst. The spe ctrum is related to the V3d-O2p hybridised unoccupied states. The overall peak position at the V L3-absorption edge is determined by the formal oxidation state of the absorbing vanadium atom. Details of the absorption fine structure are influenced by the geometric structure of the compound. Empirically we found a linear relationship between the energy position of several absorption resonances and the V -O bond length of the participating atoms. This allows to identify the contribution of specific V-O bonds to the near edge X-ray absorption fine structure. The bond length / resonance position relationship will be discussed under consideration of relations between geometric structure and NEXAFS features observed in X-ray absorption experiments and theory.

A regression tree analysis on selective oxidation of methane to methanol/formaldehyde was applied to identify fundamentals affecting catalyst performance. The electronegativity correlates with methane activation energy and formaldehyde selectivity.

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The surface of an activated vanadium phosphorus oxide (VPO) catalyst was investigated by means of in situ X-ray absorption spectroscopy in the total electron yield mode. We observed significant changes of the V L 3 -near edge X-ray absorption fine structure (NEXAFS) when the material was transferred from room temperature to working conditions at 400°C in the reaction atmosphere. We studied the same VPO material under different gas compositions comprising the reaction mixture of n-butane and oxygen, pure oxygen and vacuum to elucidate the influence of the gas-surface interaction and the effect of the temperature. The results of this extensive study indicate a dynamic response of the catalyst surface to the applied conditions.