Molybdenum oxide based structure

A. Muller, D. Fenske, and P. Kogerler, From giant molecular clusters and precursors to solid-state structures, Curr. Op. SolidState Mat. Sci. 3 141 (1999) L. Cronin, P. Kogerler, and A. Muller, Controlling growth ofnovel solid-state materials via discrete molybdenum-oxide-based building blocks as synthons, /. Solid State Chem. 152 57 (2000). 

This cluster was structurally characterized as dimer of two giant clusters with the formula Eu6A2[Moi28Eu40 38gHio(H20)8i]2 (2A = 2H" or 2K ) (68). The dimer contains two elliptical molybdenum oxide-based units, linked together by two Eu—O—Mo bonds, each unit incorporates 128 and four Eu centers and includes large fragments of the... 

Michailovski, A. and Patzke, G. R. Hydrothermal Synthesis of Molybdenum Oxide Based Materials Strategy and Structural Chemistry. Chemistry. A European Journal, 12(36), 9122-9134 (2006). 

Our work was initiated on the reduced ternary molybdenum oxides with the thought that the metal cluster electron count (MCE) should be variable for the Mo308 cluster units. Based on Cotton s previous molecular orbital treatment of such clusters (16) it appeared that MCE s from 6 to 8 could be accommodated, but it was not clear whether the seventh and eighth electrons would occupy bonding or antibonding orbitals with respect to the M-M interactions. We thus set about to determine this from structural data on suitable compounds. The attempted replacement of Zn2+ with Sc3+ to secure the compound ZntSc°Mo308 was conducted via the reaction shown in equation 1. 

CS planes across which the MoOe octahedra share edges rather than comers. These extended defects exist even at modest temperature due to the large mobility of oxygen vacancies, Further, the defects are stabilized by relaxation as a result of Mo cation displacement from their centers of symmetry to interstices. Homologous series of molybdenum oxides [1, 3, 12, 34, 154, 158, 160, 163, 164], which are based on CS plane formation starting from a ReOs-type structure, include MOn03n-i and Mon03 .2 systems. 

Oxides Compared to silica-based networks, nonsiliceous ordered meso-poious materials have attracted less attention, due to the relative difficulty of applying the same synthesis principles to non-sihcate species and their lower stability (227). Nonsiliceous framework compositions are more susceptible to redox reactions, hydrolysis, or phase transformations to the thermodynamically preferred denser crystalline phases. Template removal has been a major issue and calcination often resulted in the collapse of the mesostracture. This was the case for mesostractured surfactant composites of mngsten oxide, molybdenum oxide, and antimony oxide, and meso-structured materials based on vanadia that were obtained at early stages. Because of their poor thermal stability, none of these mesostructures were obtained as template-free mesoporous solids (85, 228, 229). 

K. Chen, S. Xie, A.T. Bell and E. Iglesia, Structure and properties of oxidative dehydrogenation catalysts based on M0O3/AI2O3, J. Catal, 198(2), 232-242, 2001. H.C. Hu and l.E. Wachs, Catalytic properties of supported molybdenum oxide catalysts In situ Raman and methanol oxidation studies, J. Phys. Chem., 99(27), 10911-10922, 1995. 

Goutenoire F, Isnard O, Suard E, Bohnke O, Lahgant Y, Retoux R and Lacorre P (2001), Structural and transport characteristics of the LAMOX family of fast oxide-ion conductors, based on lanthanum molybdenum oxide LajMojO, , / Mater Chem, 11,119-124. 

The modeling of molybdenum-based classical catalysts supported on alumina was improved by the use of calculations with periodic boundary conditions [10, 49, 52], which better represent the alumina surface [67]. It became possible to describe the relative stabilities of the different surface sites, including the effect of temperature and water pressure. The more stable (110) and (100) alumina surfaces were considered, and the investigation focused on the structure of the potential initial molybdenum-oxide monomeric and dimeric species, as well as the corresponding methylidene species and their reactivity with ethene [10,49]. 

The process has been commercially implemented in Japan since 1977 [1] and a decade later in the U.S., Germany and Austria. The catalysts are based on a support material (titanium oxide in the anatase form), the active components (oxides of vanadium, tungsten and, in some cases, of molybdenum) and modifiers, dopants and additives to improve the performance, especially stability. The catalyst is then deposited over a structured support based on a ceramic or metallic honeycomb and plate-type structure on which a washcoat is then deposited. The honeycomb form usually is an extruded ceramic with the catalyst either incorporated throughout the stmcture (homogeneous) or coated on the substrate. In the plate geometry, the support material is generally coated with the catalyst. 

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