Molecular precursor route to bulk and silica-supported Nb2Mo3O14 using water-soluble oxo-oxalato complexes

The catalytically relevant Nb2Mo3O14 phase has been prepared in bulk and silica-supported forms via the so-called "multiple molecular precursors method" from water-soluble oxo-oxalato complexes of Nb and Mo, (NH4)3[NbO(ox)3].H2O, and (NH4)2[MoO3(ox)].H2O. Thermal treatment of the mixed Nb-Mo precursor has been optimized for the formation of the pure Nb2Mo3O14 phase, either as bulk oxide or a silica-supported phase with high specific surface area. A characterization of the bulk phase obtained via the conventional ceramic route has also been carried out and a comparison has been made with the precursors route. According to this route, the Nb2Mo3O14 phase is shown to be formed in a pure form at 700 degrees C (i.e., 100 degrees C below the lowest temperature reported so far for the formation of the phase by the ceramic method). The supported samples have appreciable specific surface areas of 60-70 m(2) g(-1), much larger than those reached in the previous attempts under vacuum in sealed vials. The SEM and EDX analyses reveal a high dispersion of the desired phase on the silica support.     

铬和钼掺杂对HCa2Nb3O10/Pt光催化性能的影响

通过高温固相反应合成了铌酸盐KCa2Nb3O10及Cr3+和Mo6+掺杂(摩尔分数5%)的KCa2Nb3O10,并通过离子交换反应制备出HCa2Nb3O10及Cr3+和Mo6+掺杂的HCa2Nb3O10,采用X射线衍射、原子吸收光谱、扫描电镜等对所制得的样品进行了表征.在甲醇为电子给体、Pt为助催化剂的情况下,研究了催化剂HCa2Nb3O10及Cr3+和Mo6+掺杂的HCa2Nb3O10在紫外光辐射下分解水产氢的光催化活性,并讨论了引起催化剂活性差异的原因.     

Das Mischungsverhalten von Nb3Sn mit Mo3Si,Mo3Ge und Nb3Ge

Zusammenfassung Mittels homogenisierter Sinter-und Schmelzproben wird die Bildung von lückenlosen Mischreihen zwischen Nb₃Sn mit Mo₃Si, Mo₃Ge und Nb₃Ge nachgewiesen.Mit 1 Abbildung     

New data on protonation and hydration of perovskite-type layered oxide KCa2Nb3O10

Journal of Thermal Analysis and Calorimetry - Protonation and hydration processes of layered perovskite-like oxide KCa2Nb3O10 during the reaction with nitric acid solutions with different...     

Co-K and Mo-K edges Quick-XAS study of the sulphidation properties of Mo/Al2O3 and CoMo/Al2O3 catalysts

The sulphidation process of two catalysts (Mo/Al₂O₃ and CoMo/Al₂O₃) has been investigated by time-resolved X-ray Absorption Spectroscopy. With the unique edge jumping capability available at the SOLEIL synchrotron, studies of cobalt and molybdenum species have been conducted simultaneously on the same bimetallic catalyst. A methodology combining Principal Component Analysis and Multivariate Curve Resolution with Alternating Least Squares methods unravels a 3-stepped or 4-stepped sulphidation process for the bimetallic and monometallic catalysts, respectively. An oxysulphide-based molybdenum species has been identified as an intermediate for Mo/Al₂O₃ and a MoS₃-like species has been observed for both catalysts.     

ChemInform Abstract: Synthesis and Characterization of K3Mo14O22, K1.66Pb1.34Mo14O22, and K1.29Sn1.71Mo14O22: Oligomeric Clusters with Three Trans Edge-Shared Mo Octahedra.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.     

Activation and properties of Mo=O bonds in Mo/SiO2 catalysts

The existence of the charge transfer excited triplet state [Mo⁵⁺-O^-] produced by UV-irradiation of Mo/SiO₂ catalysts, and its reactivity are evidenced by experiments of photoluminescence, photoinduced metathesis, and photoreduction of CO. Mo⁵⁺ ions can be produced separately by thermal activation and O^- ions by further adsorption of N₂O on those Mo⁵⁺ ions. The latter of which are adsorbed on Mo⁶⁺ ions are found to be more reactive than O^2- of [Mo⁶⁺ =O^2-] bond. They are able either to add a molecule such as CO or C₂H₄, or to abstract hydrogen from H₂, CH₄ or trans-dicyanoethylene, or a CN group form tetracyanoethylene (TCNE). The Mo⁵⁺ ions are able to coordinate gas phase ligands when their coordination sphere possesses vacant sites. This is the case for tetracoordinated Mo⁵⁺ _4c ions arising from reduction of tetrahedral Mo⁶⁺ ions (Eq. (7)). These Mo⁵⁺ _4c ions are similar to those produced by UV-irradiaiion (Eq. (2)). In addition, if the adsorbed molecule has a sufficiently large electron affinity, such as TCNE or O₂, an electron transfer can occur (Eq. (9) and (17)). The [Mo⁵⁺-O^-] bond obtained by thermal activation is more difficult to evidence than that obtained with UV-activation because it is not detectable by EPR. However, the EPR results obtained at low temperature show that the O^- ions adsorbed on Mo/SiO₂ catalysts as well as the [Mo⁵⁺-O^-] excited triplet state obtained by UV-irradiation of 1Mo⁶⁺=O²] interact with methanol (Eq. (16)). They are consistent with the mechanism of methanol oxidation occurring at high temperature (Eq. (4)).     

Das Ternare System Nb2O5-Li2O-Sc2O3

Zusammenfassung Es wird ein isothermer Schnitt im System Nb₂O₅ -Li₂O-Sc₂O₃ untersucht. Dabei wurde die neue Verbindung Li_0.5Sc_0.5Nb₂O₆ gefunden. Die Röntgenreflexionsaufnahmen ergaben unter Annahme eines orthorhombischen Gitters die Parameter a=1433.6/2/ pm, b=572.96/6/ pm und c=505.76/4/ pm.Bei 1453 K wurde der LiNbO₃-Homogenitätsbereich bestimmt, der sich vom binären System Li₂O-Nb₂O₅ bis zu 5 mol% Sc₂O₃ im Dreikomponentensystem erstreckt. Im Homogenitätsbereich wurde die Variation der Gitterkonstanten gemessen. Das Volumen der Elementarzelle nimmt mit steigendem Sc₂O₃-Gehalt zu.

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An isothermal section was investigated in the system Nb₂O₅-Li₂O-Sc₂O₃. The new compound Li_0.5Sc_0.5Nb₂O₆ was found The x-ray reflection pattern could be indexed with the assumption of an orthorhombic lattice with the parameters of a=1433.6(2) pm, b=572.96(6) pm, c=505.76(4) pm.The LiNbO₃-homogeneity range was determined at 1453 K. It extends from the binary Li₂O-Nb₂O₅ to 5 mole-% Sc₂O₃ in the ternary system. The variation of the lattice constants of LiNbO₃ was measured in the homogeneity range. The volume of the unit cell increases with increasing content of Sc₂C₃.

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Nb₂O₅-Li₂O-Sc₂O₃, Li_0,5 Sc_0,5Nb₂O₆. , $ = 1433,6/2/ , =572,96/6/ =505,76/4/ . 1453 LiNbO₃, $ Li₂O-Nb₂₅ $ 5 %. $ . .

     

Structure and Crystallographic Disorder of [Mo2(O2CCF3)2I4](HPPh3)2

The reaction of Mo₂(O₃CCF₃)₄ with (CH₃)₃SiI and PPh₃ gave the title complex [Mo₃(O₂CCF₃)₂I₄]-(HPPh₃)₂ which was characterized by X-ray crystallography. Crystal data for [Mo₂(O₂CCF₃)₂I₄](HPPh₃)₂: space group $ {\rm P}\bar 1 $, a = 10.953(4) Å, b = 12.784(3) Å, c = 19.829(4) Å, α = 100.68(2)°, β = 91.16(2)°, γ = 112.98(2)°, V = 2498.6(10) ų, Z = 2, with final residuals R = 0.0887 and Rw = 0.0965. There are two independent molecules in each asymmetric unit. The molybdenum, oxygen, and fluoride atoms in one of the two independent molecules are disordered, such that the primary set is 53% occupied, and the secondary set 47%.