Mo3O5(OH)(2)(AsO4)2: A new solid with a structure related to beta VOPO4

Mo3O5(OH)(2)(AsO4)(2) was prepared at 100 degrees C from an aqueous solution of MoO3 containing arsenic and nitric acids. It crystallises in the monoclinic system, a = 13.024(1)Angstrom, b = 7.2974 (2) Angstrom, c = 13.281(1) Angstrom, beta = 121.124(8)degrees, Z = 4, space group C2/c. The structure was determined by Rietveld refinement from X-ray powder diffraction data. The three-dimensional structure is built up from MoO6 and MoO5OH octahedra and AsO4 tetrahedra sharing corners. The octahedra share two opposite vertices forming zigzag chains that run parallel to [10(1) over bar]. Each AsO4 tetrahedron is connected to four octahedra, two of which belong to the same chain, thus linking three chains. The resulting covalent framework is similar to that of beta VOPO4 in which one tetrahedral P site for every three is empty. The two protons are likely to be bonded to two (out of four) unshared oxygen atoms surrounding this empty site. All the Mo atoms are strongly off-centred in the octahedra; and the off-centring is disordered. The disorder is discussed in terms of Mo shifts perturbed by a disordered hydrogen bonding scheme.

Oxide nanotubes prepared using carbon nanotubes as templates

Hollow nanotubes of SiO2, Al2O3, V2O5, and MoO3 have been prepared using carbon nanotubes as templates. The procedure involves coating the carbon nanotubes with tetraethylorthosilicate, aluminum isopropoxide, or vanadium pentoxide gel, followed by calcination and heating at higher temperatures in air to oxidize the carbon. SiO2 nanotubes containing transition metal ions have been prepared by this procedure since such materials may be of use in catalysis.

Reaction of La2CuO4 with binary metal oxides in the solid state: Metathesis, addition, and redox metathesis pathways

Investigation of the reaction of La2CuO4 with several binary metal oxides in the solid state at elevated temperatures has revealed three different reaction pathways. Reaction of La2CuO4 with strongly acidic oxides such as Re2O7, MoO3, and V2O5 follows a metathesis route, yielding a mixture of products: La3ReO8/La2MoO6/LaVO4 and CuO. Oxides such as TiO2, MnO2, and RuO2 which are not so acidic yield addition products: La2CuMO6 (M = Ti, Mn, Ru). SnO2 is a special case which appears to follow a metathesis route, giving La2Sn2O7 pyrochlore and CuO, which on prolonged reaction transform to the layered perovskite La2CuSnO6. The reaction of La2CuO4 with lower valence oxides VO2 and MoO2, on the other hand, follows a novel redox metathesis route, yielding a mixture of LaVO4/LaCuO2 and La2MoO6/Cu, respectively. This result indicates that it is the redox reactivity involving V-IV + Cu-II --> V-V + Cu-I and Mo-IV + Cu-II --> Mo-VI + Cu-0, and not the acidity of the binary oxide, that controls the nature of the products formed in these cases. The general significance of these results toward the synthesis of complex metal oxides containing several metal atoms is discussed.

Molybdenum trioxide catalyzed oxidative cross-dehydrogenative coupling of benzylic sp(3) C-H bonds: synthesis of alpha-aminophosphonates under aerobic conditions

Molybdenum trioxide (MoO3) catalyzed efficient oxidative cross-dehydrogenative-coupling (CDC) method for C-H functionalization of N-aryl tetrahydroisoquinolines has been explored. This user-friendly method of synthesizing alpha-aminophosphonates employs 1.1 equiv of dialkyl-H-phosphonate under aerobic condition. Formation of new C-P bonds from unfunctionalized starting materials under environmentally benign conditions provides an excellent avenue for the synthesis of biologically active alpha-aminophosphonates. (C) 2012 Elsevier Ltd. All rights reserved.

About the transparent electrode of the organic photovoltaic cells

Electrodes and the nature of their contact with organic materials play a crucial role in the realization of efficient optoelectronic components. Whether the injection (organic light-emitting diodes - OLEDs) or collection (organic photovoltaic cells - OPV cells) of carriers, contacts must be as efficient as possible. To do this, it is customary to refer to electrode surface treatment and/or using a buffer layer all things to optimize the contact. Efficiency of organic photovoltaic cells based on organic electron donor/organic electron acceptor junctions can be strongly improved when the transparent conductive anode is coated with a buffer layer (ABL). We show that an ultra-thin gold (0.5 nm) or a thin molybdenum oxide (3-5 nm) can be used as efficient ABL. However, the effects of these ABL depend on the highest occupied molecular orbital (HOMO) of different electron donors of the OPV cells. The results indicate that, in the case of metal ABL, a good matching between the work function of the anode and the highest occupied molecular orbital of the donor material is the major factor limiting the hole transfer efficiency. Indeed, gold is efficient as ABL only when the HOMO of the organic donor is close to its work function Phi(Au). MoO3 has a wider field of application as ABL than gold. The role of the oxide is not so clearly understood than that of Au, different models proposed to interpret the experimental results are discussed.

Mechanistic Aspects for the Formation of Copper Dimer Bridged by Phosphonic Acid and Extending Its Dimensionality by Organic and Inorganic Linkers: Synthesis, Structural Characterization, Magnetic Properties, and Theoretical Studies

Six new copper metal complexes with formulas Cu(H2O)(2,2'-bpy) (H2L)](2) center dot H4L center dot 4 H2O (1), {Cu(H2O)(2,2'-bpy)-(H3L)}(2)(H2L)]center dot 2H(2)O (2), Cu(H2O)(1,10-phen)(H2L)](2)center dot 6H(2)O (3), Cu(2,2'-bpy)(H2L)](n)center dot nH(2)O (4), Cu(1,10-phen)(H2L)](n)center dot 3nH(2)O (5), and {Cu(2,2'-bpy)(MoO3)}(2)(L)](n)center dot 2nH(2)O (6) have been synthesized starting from p-xylylenediphosphonic acid (H4L) and 2,2'-bipyridine (2,2'-bpy) or 1,10-phenanthroline (1,10-phen) as secondary linkers and characterized by single crystal X-ray diffraction analysis, IR spectroscopy, and thermogravimetric (TG) analysis. All the complexes were synthesized by hydrothermal methods. A dinuclear motif (Cu-dimer) bridged by phosphonic acid represents a new class of simple building unit (SBU) in the construction of coordination architectures in metal phosphonate chemistry. The initial pH of the reaction mixture induced by the secondary linker plays an important role in the formation of the molecular phosphonates 1, 2, and 3. Temperature dependent hydrothermal synthesis of the compounds 1, 2, and 3 reveals the mechanism of the self assembly of the compounds based on the solubility of the phosphonic acid H4L. Two-dimensional coordination polymers 4, 5, and 6, which are formed by increasing the pH of the reaction mixture, comprise Cu-dimers as nodes, organic (H2L) and inorganic (Mo4O12) ligands as linkers. The void space-areas, created by the (4,4) connected nets in compounds 4 and 5, are occupied by lattice water molecules. Thus compounds 4 and 5 have the potential to accommodate guest species/molecules. Variable temperature magnetic studies of the compounds 3, 4, 5, and 6 reveal the antiferromagnetic interactions between the two Cu(II) ions in the eight membered ring, observed in their crystal structures. A density functional theory (DFT) calculation correlates the conformation of the Cu-dimer ring with the magnitude of the exchange parameter based on the torsion angle of the conformation.

Synergistic Effect of Mo plus Cu Codoping on the Photocatalytic Behavior of Metastable TiO2 Solid Solutions

Codoping with Cu and Mo is shown to have a synergistic effect on the photocatalytic activity of TiO2. The enhancement in activity is observed only if the synthesis route results in TiO2 in which (Cu, Mo) codopants are forced into the TiO2 lattice. Using X-ray photoelectron spectroscopy, Cu and Mo are shown to be present in the +2 and +6 oxidation states, respectively. A systematic study of the ternary system shows that TiO2 containing 6 mol % CuO and 1.5 mol % MoO3 is the most active ternary composition. Ab initio calculations show that codoping of TiO2 using (Mo, Cu) introduces levels above the valence band, and below the conduction band, resulting in a significant reduction in the band gap (similar to 0.8 eV). However, codoping also introduces deep defect states, which can have a deleterious impact on photoactivity. This helps rationalize the narrow compositional window over which the enhancement in photocatalytic activity is observed.

Tandem organic light-emitting diodes with an effective charge-generation connection structure

The tandem organic light-emitting diodes (OLEDs) with an effective charge-generation connection structure of Mg-doped tris(8-hydroxyquinoline) aluminum (Alq(3))/Molybdenum oxide (MoO3)-doped 3, 4, 9, 10-perylenetetracarboxylic dianhydride (PTCDA) were presented. At a current density of 50 mA/cm(2), the current efficiency of the tandem OLED with two standard NPB/Alq(3) emitting units is 4.2 cd/A, which is 1.7 times greater than that of the single EL device. The tandem OLED with the similar connection structure of Mg-doped PTCDA/MoO3-doped PTCDA was also fabricated and the influences of the different connection units on the current efficiency of the tandem OLED were discussed as well.

新型固体酸催化剂的设计制备及其性能研究

酸催化剂可以用来催化烃类裂解、重整、异构、烯烃水和、烷基化和酯化等重要化学反应，在石油炼制和石油化工领域有极其广泛的应用。与传统液体酸相比，新型固体酸催化剂具有容易与反应物和产物分离、易再生、不腐蚀反应器、环境污染少等优点，因此研究开发环境友好的新型固体酸催化剂成为国际上催化领域研究的热点。本论文研究新型固体酸催化剂的酸强度和延长催化剂使用寿命的方法，具有很高的工业实用价值和理论意义。 研究了固体酸催化剂在正己烷异构化和异丁醇脱水这两个反应的催化活性，结果显示：1）复合超强酸催化剂，2）Hβ及其负载催化剂，3）负载杂多酸，4）ZrO2·Bi2O3、ZrO2·CaO四类催化剂酸强度较高且强度大小为:1＞2≈3＞4。氢溢流的引入提高了Pt-SO42-/ ZrO2催化剂在反应中的催化活性,一定程度上弥补了酸强度的不足，也使一些原本没活性的催化剂有了一定的活性，如MOO3催化剂。 研究了异丁烷在12wt%V2O5/γ-Al2O3催化剂上脱氢制异丁烯的反应和异丁烯在50wt%HSiW/SiO2、Amberlyst-15和Amberlyst-35树脂催化剂上的迭代反应，均获得了较好的催化活性。 首次将催化剂表面的疏油性应用在酸催化领域，在硅胶负载的钨硅酸中掺杂不同含量聚四氟乙烯制备出具有一定疏油性的催化剂，用异丁烯迭代反应作为探针反应着重研究了催化剂表面的适当疏油性对催化剂的寿命和产物选择性的影响。结果显示催化剂表面的疏油性不仅提高了C8 =的选择性并且有效延长催化剂寿命。这主要是由于催化剂表面具有适当的疏油性，反应的中间产物C8=易于从具有疏油性的表面脱附，减少了C8=继续在催化剂表面进行连续反应生成C12=和C16=的机会，因此提高了C8=的选择性。这可能促进了更高的产物选择性，低的积炭量和较长的催化剂使用寿命。 研究了催化剂表面的疏水疏油性在醋酸与正丁醇的酯化反应中的应用。结果显示，当酯化反应产物为液相时，催化剂表面的疏水疏油性非常有利于产物从催化剂表面脱附，能有效提高正丁醇的转化率。 关键词：酸强度，钨硅酸，聚四氟乙烯，疏油性，寿命

Structure and acidity of Mo/H-MCM-22 catalysts studied by NMR spectroscopy

A comprehensive study on physical and chemical properties of Mo/MCM-22 bifunctional catalysts has been made by using combined analytic and spectroscopic techniques, such as adsorption, elemental analysis, and Xe-129 and P-31 NMR of adsorbed trialkylphosphine oxide probe molecules. Samples prepared by the impregnation method with Mo loadings ranging from 2-10 wt.% have been examined and the results are compared with that obtained from samples prepared by mechanical mixing using MoO3 or Mo2C as agents. Sample calcination treatment is essential in achieving a well-dispersed metal species in Mo/MCM-22. It was found that, upon initial incorporation, the Mo species tend to inactivate both Bronsted and Lewis sites locate predominantly in the supercages rather than the 10-membered ring channels of MCM-22. However, as the Mo loading exceeds 6 wt.%, the excessive Mo species tend to migrate toward extracrystalline surfaces of the catalyst. A consistent decrease in concentrations of acid sites with increasing Mo loading < 6 wt.% was found, especially for those with higher acid strengths. Upon loading of Mo > 6 wt.%, further decreases in both Bronsted and Lewis acidities were observed. These results provide crucial supports for interpreting the peculiar behaviors previously observed during the conversion of methane to benzene over Mo/MCM-22 catalyst under non-oxidative conditions, in which an optimal performance was achieved with a Mo loading of 6 wt.%. The effects of Mo incorporation on porosity and acidity features of the catalyst are discussed. (C) 2004 Published by Elsevier B.V.

Identifying the isolated transition metal ions/oxides in molecular sieves and on oxide supports by UV resonance Raman spectroscopy

Isolated transition metal ions/oxides in molecular sieves and on surfaces are a class of active sites for selective oxidation of hydrocarbons. Identifying the active sites and their coordination structure is vital to understanding their essential role played in catalysis and designing and synthesizing more active and selective catalysts. The isolated transition metal ions in the framework of molecular sieves (e.g., TS-1, Fe-ZSM-5, and V-MCM-41) or on the surface of oxides (e.g., MoO3/Al2O3 and TiO2/SiO2) were successfully identified by UV resonance Raman spectroscopy. The charge transfer transitions between the transition metal ions and the oxygen anions are excited by a UV laser and consequently the UV resonance Raman effect greatly enhances the Raman signals of the isolated transition metal ions. The local coordination of these ions in the rigid framework of molecular sieves or in the relatively flexible structure on the surface can also be differentiated by the shifts of the resonance Raman bands. The relative concentration of the isolated transition metal ion/oxides could be estimated by the intensity ratio of Raman bands. This study demonstrates that the UV resonance Raman spectroscopy is a general technique that can be widely applied to the in-situ characterization of catalyst synthesis and catalytic reactions. (C) 2003 Elsevier Science (USA). All rights reserved.

In situ FT-IR spectroscopic studies of CO adsorption on fresh Mo2C/Al2O3 catalyst

The surface sites of supported molybdenum carbide catalyst derived from different synthesis stages have been studied by in situ FT-IR spectroscopy using CO as the probe molecule. Adsorbed CO on the reduced passivated Mo2C/Al2O3 catalyst gives a main band at 2180 cm(-1), which can be assigned to linearly adsorbed CO on Mo4+ sites. The IR results show that the surface of reduced passivated sample is dominated by molybdenum oxycarbide. However, a characteristic IR band at 2054 cm-1 was observed for the adsorbed CO on MoO3/Al2O3 carburized with CH4/H-2 mixture at 1033 K (fresh Mo2C/Al2O3), which can be assigned to linearly adsorbed CO on Modelta+ (0 < delta < 2) sites Of Mo2C/Al2O3, Unlike adsorbed CO on reduced passivated Mo2C/Al2O3 catalyst, the IR spectra of adsorbed CO on fresh Mo2C/Al2O3 shows similarity to that on some of the group VIII metals (such as Pt and Pd), suggesting that fresh carbide resembles noble metals. To study the stability Of Mo2C catalyst during H-2 treatment and find proper conditions to remove the deposited carbon species, H-2 treatment of fresh Mo2C/Al2O3 catalyst at different temperatures was conducted. Partial amounts of carbon atoms in Mo2C along with some surface-deposited carbon species can be removed by the H, treatment even at 450 K. Both the surface-deposited carbon species and carbon atoms in carbide can be extensively removed at temperatures above 873 K.

Catalytic decomposition of hydrazine over supported molybdenum nitride catalysts in a monopropellant thruster

The catalytic decomposition of hydrazine over a series of MoNx/gamma-Al2O3 catalysts with different Mo loadings was investigated in a monopropellant thruster (10 N). When the Mo loading is equal to or higher than the monolayer coverage of MoO3 on gamma-Al2O3, the catalytic performance of the supported molybdenum nitride catalyst is close to that of the conventionally used Ir/gamma-Al2O3 catalyst. The MoNx/gamma-Al2O3 catalyst with a loading of about 23wt% Mo (1.5 monolayers) shows the highest activity for hydrazine decomposition. There is an activation process for the MoNx/gamma-Al2O3 catalysts at the early stage of hydrazine decomposition, which is probably due to the reduction of the oxide layer formed in the passivation procedure.

On the induction period of methane aromatization over Mo-based catalysts

The behavior of different species during the temperature-programmed surface reaction (TPSR) of methane over various catalysts is traced by an online mass spectrometer, It is demonstrated that the transformation of MoO3 to molybdenum carbide hinders the activation of methane as well as the succeeding aromatization in the TPSR, If this transformation process is done before the reaction, the temperature needed for methane activation and benzene formation will be greatly lowered (760 and 847 K, respectively). On the basis of comparison of the catalytic behavior of molybdenum supported on different zeolites, it is suggested that the initial activation of methane is the rate-determining step of this reaction. For the cobalt catalysts supported on HMCM-22 or Mo catalysts supported on TiO2, no benzene formation could be observed during the TPSR, However, the prohibition of benzene formation is different in nature over these two catalysts: the former lacks the special properties exhibited by molybdenum carbide, which can continuously activate methane even when multiple layers of carbonaceous species are formed on its surface, while the latter cannot accomplish the aromatization reaction since there are no Bronsted acid sites to which the activated intermediates can migrate, although the activation of methane can be achieved on it. Only for the catalysts that possess both of these properties, together with the special channel structure of zeolite, can efficient methane aromatization be accomplished. (C) 2000 Academic Press.