Mixed oxides composed of the four metals Mo, V, Te, and Nb are known to be efficient catalysts in selective oxidation of lower alkanes. The outstanding catalytic performance of such mixed oxides is attributed to the presence of the so-called M1 crystal phase that contains all four elements in the metal positions of the structure. In the present work, an M1 phase composed only of Mo and V has been prepared by hydrothermal synthesis. High crystallinity was achieved by applying a synthesis temperature of 200 °C. The phase-pure mixed MoV oxide was studied as catalyst in the oxidation of propane. In contrast to previous reports, the desirable oxidation product acrylic acid is formed over the Te-free M1 structure in significant amounts, implying that Te is not necessarily required as a component of the active ensemble responsible for selective oxygen insertion. The MoV M1 oxide is, however, less selective compared to that of the M1 structure composed of the four metals Mo, V, Te, and Nb. The reason has been determined by applying a combination of synchrotron-based single crystal structure analysis and near-ambient-pressure X-ray photoelectron spectroscopy. Determination of the crystal structure of MoV M1 oxide reveals partial occupation of sites in the hexagonal channels of the M1 structure by V, which are occupied by Te in MoVTeNb M1 oxide. Hydrolysis of the M-O bonds (M = V, Te) under reaction conditions leads to migration of the metal in the hexagonal channels to the surface. Accumulation of more than 50 at % V on the surface of the MoV M1 oxide most likely causes postcombustion of formed acrylic acid, whereas enrichment of Te at the surface of MoVTeNb M1 oxide results in dilution of surface V5+ species and, consequently, high selectivity

No abstract

The crystal structures of H2SO4 and (H30)(HSO4) have been refined with good accuracy (R = 0.021 and 0.033, respectively) making a discussion of hydrogen bonding now possible. In sulfuric acid, the S--O and S--OH distances are 1.426 (1) and 1.537 (1) A,, respectively, and the structure is characterized by layers of hydrogenconnected SO4 tetrahedra forming 44 nets. In oxonium hydrogensulfate, the HSO4-tetrahedra form infinite hydrogen-bonded chains which are linked by H3 O÷ ions to form double layers. CommentMany new acidic sulfates of mono-and divalent metals have recently been synthesized and structurally char-

SiCl4 · 2 Py kristallisiert in der Raumgruppe C2/m mit 2 Formeleinheiten pro Elementarzelle. Das trans‐oktaedrische Molekül besitzt 2/m‐Symmetrie. Die SiCl‐Abstände betragen 218,3 pm und sind damit um 9,2% länger als im tetraedrischen SiCl4. Diese Bindungsschwächung senkt die Aktivierungsenergie des Halogenaustausches am Silicium. (SiI2Py4)I2 kristallisiert trigonal‐rhomboedrisch mit 3 Formeleinheiten pro Elementarzelle.

No abstract