Reduced Molybdenum Oxide Research Articles

XPS study of as-prepared and reduced molybdenum oxides

The surface properties of Mo oxides (MoO 2 and MoO 3) were investigated using X-ray photoelectron spectroscopy (XPS). As-prepared MoO 3 showed two well resolved spectral lines at 232.5 and 235.6 eV, which were assigned to the Mo 3d 5/2, 3d 3/2 spin-orbit components, respectively. After the sample was reduced with H 2 at 673 K for 3 h, 76% of the MoO 3 present on the surface was transformed to MoO 2. Hydrogen reduction of MoO 2 produced a new state (Mo δ+, 0 < δ < 4) at a binding energy of 228.7 ± 0.2 eV. We assigned this new state to Mo 3+ based on our binding energy assignments for Mo 0, Mo 4+, Mo 5+, and Mo 6+. The concentration of Mo δ+ state increased with increasing reduction time and this state was suggested to contain hydrogen, which may be a necessary requisite for desulfurization and denitrogenation reactions.

Synthesis and Characterization of K0.19Ba3.81Mo22O34: A Quaternary Reduced Molybdenum Oxide Containing Metal-Metal Bonded Oligomers with Five Trans Edge-Shared Molybdenum Octahedra

Crystals of K0.19Ba3.81Mo22O34, a metal-metal bonded oligomer in the series Mn-xMO4n+2O6n+4 with n = 5, have been synthesized. The Mo22 clusters consist of five trans edge-shared Mo octahedra. The dominant features of K0.19Ba3.81Mo22O34 include four short and four long apical-apical Mo bond distances within the cluster, relatively long intercluster metal-metal bond distances (>2.99 Å), and cluster interconnections which have a stair-step arrangement from one Mo22 unit to the next. K0.19Ba3.81Mo22O34 crystallizes in the centrosymmetric space group P21/a, with lattice parameters of a = 9.908(2) Å, b = 9.353(2) Å, c = 15.951(3) Å, β = 98.78(2)°, Vol = 1460.8(4) Å3, Z = 2, and R = 0.0493 (Rw = 0.0603) for 2768 reflections with I > 3.5σ(I). Five cations per formula unit can be accommodated in the pockets created by the interconnected Mo22O50 clusters. However, this phase has four fully occupied cation sites and one vacancy. The number of electrons available for metal-metal bonding (MCE) was derived from Mo-O bond valence sums around the molybdenum atoms (72(2)) and is in good agreement with the value calculated from format oxidation states (71.8e). Mo-Mo bond order sums, excluding intercluster metal-metal interactions, although slightly high (MCE = 72.8(5)), indicate maximum utilization of electrons for Mo-Mo bonding. The magnetic susceptibility of this compound indicates that it is spin-paired with a small paramagnetic tail at low temperatures and a large residual χTIP above 50 K. Electron spin resonance results indicate that the paramagnetic tail may be arising from molybdenum containing impurities, or defects, on which electrons are trapped. Structural and electronic comparisons to two known pentameric oligomers are discussed.

High-Resolution Electron Microscopy of condensed clusters in a potassium barium oxomolybdate

The recently synthesized compound K0.19Ba3.81Mo22O34 is a representative of the ternary and quaternary reduced molybdenum oxides in which clusters built from molybdenum octahedra are arranged in layers of composition AxByMo4n+2O6n+4. The number of trans-edgesharing molybdenum octahedra in the cluster is represented by n. The general concept of cluster condensation is formulated and discussed elsewhere. For K0.19Ba3.81Mo22O34, n is equal to 5. A ternary representative, likewise with n = 5, is In6Mo22O34.By x-ray structure analysis, K0.19Ba3.81Mo22O34 proved to crystallize in space group P21/a with parameters a = 0.9908(2) nm, b = 0.9353(2) nm, c = 1.5951(3) nm, and β = 98.78(2)°. The potassium atoms were found to reside on the same sites as the barium atoms with an almost statistical distribution.We studied K0.19Ba3.81Mo22O34 by high-resolution electron microscopy (HREM). Small fragments of a crystal were investigated using a Philips CM30/ST microscope operating at 300 kV (point resolution 0.19 nm). At appropriate orientations of the crystal fragments, HREM images reveal domains of two ordered polytypes: a monoclinic and an orthorhombic one (Figs. 1 and 2).

Multifrequency ESEEM spectroscopy of ammonia adsorbed on silica-supported reduced molybdenum oxide

The structural environment of a Mo 5+ center on silica-supported molybdenum oxide, with adsorbed ammonia, was probed by ESEEM spectroscopy. Features attributable to 1 H and 14 N are observed in the spectra and indicate the direct coordination of ammonia to the Mo 5+ . Nuclear hyperfine and quadrupole coupling constants, elicited by multifrequency ESEEM techniques, are compared with ones recently determined by us for the analogous vanadium oxide system (J. Phys. Chem. 1992, 96, 9007)

Catalytic cooperation between MoO 3 and Sb 2O 4 in N-ethyl formamide dehydration II. Nature of active sites and role of spillover oxygen

The present work reports experiments designed to further investigate the role of MoO 3 and Sb 2O 4 in the cooperative effect they exhibit in N-ethyl formamide dehydration. Temperature-programmed desorption of NH 3 showed that Bronsted acid sites are responsible for activity. TPD of CO 2 gave no indication of basic sites. The Brønsted sites are sensitive to reduction and reoxidation. Thermoreoxidation of previously reduced molybdenum oxide and oxidation of carbon deposited on MoO 3 are more rapid when α-Sb 2O 4 is admixed. The interpretation of the phenomenon is that α-Sb 2O 4 dissociates molecular O 2 to an oxygen spillover species which can maintain MoO 3 at a high degree of oxidation and, if necessary, reoxidize it or remove deposited carbon. Brønsted sites necessitate a high degree of oxidation and their number is consequently promoted by spillover oxygen. Mechanisms are proposed for the dissociation of oxygen, the reoxidation of pre-reduced MoO 3, and the formation of Brønsted acid sites. The importance of the reported results for selective oxidation or multicomponent catalysts is discussed.

Preparation of reduced molybdenum oxides (MoO 2MoO 3) by a sol-gel method

Molybdenum oxides were prepared by a sol-gel method using molybdenum chloro-ethoxide as a precursor. MoCl 5, ethanol and potassium metal were used as starting materials. KCl by-product was filtered out. All reactions proceeded in methane dichloride solvent at room temperature. Blue amorphous precipitates which look like “molybdenum blue” were obtained after evaporation of solvent. This product crystallized to MoO 3 on heating to 300 °C in air, to MoO 2 on heating in vacuum and to Mo 4O 11 together with MoO 3 and MoO 2 when heated in He gas. The valence of molybdenum in the blue, as-prepared sample, ranges from 4 to 6 and could not be determined unambiguoulsy by IR and XPS spectra. The molybdenum oxide products incorporated 25–35 wt% of physically adsorbed solvent and/or reaction product (H 2O, C 2H 5OH) and retained ethoxy and hydroxyl groups; the adsorbed species and retained ethoxy groups are lost on heating at ∼200 °C and at ∼400 °C, respectively. About 1–6 wt% of chlorine was also retained in the product, most of which was removed on heating to 160 °C in air.

ChemInform Abstract: Homologation, Hydrogenolysis, and Dehydrogenation of Ethane on SiO2‐ and SiO2‐Al2O3‐Supported Reduced Molybdenum Oxide Catalysts.

ChemInformVolume 19, Issue 9 Preparative Organic Chemistry ChemInform Abstract: Homologation, Hydrogenolysis, and Dehydrogenation of Ethane on SiO2- and SiO2-Al2O3-Supported Reduced Molybdenum Oxide Catalysts. A. K. GHOSH, A. K. GHOSH Res. Inst. Catal., Hokkaido Univ., Sapporo 060, Jap.Search for more papers by this authorK. TANAKA, K. TANAKA Res. Inst. Catal., Hokkaido Univ., Sapporo 060, Jap.Search for more papers by this authorI. TOYOSHIMA, I. TOYOSHIMA Res. Inst. Catal., Hokkaido Univ., Sapporo 060, Jap.Search for more papers by this author A. K. GHOSH, A. K. GHOSH Res. Inst. Catal., Hokkaido Univ., Sapporo 060, Jap.Search for more papers by this authorK. TANAKA, K. TANAKA Res. Inst. Catal., Hokkaido Univ., Sapporo 060, Jap.Search for more papers by this authorI. TOYOSHIMA, I. TOYOSHIMA Res. Inst. Catal., Hokkaido Univ., Sapporo 060, Jap.Search for more papers by this author First published: March 1, 1988 https://doi.org/10.1002/chin.198809076AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume19, Issue9March 1, 1988 RelatedInformation

Homologation, hydrogenolysis, and dehydrogenation of ethane on SiO 2- and SiO 2Al 2O 3-supported reduced molybdenum oxide catalysts

Kinetics and reaction mechanisms of homologation, hydrogenolysis, and dehydrogenation of ethane were studied on reduced molybdenum oxides supported on SiO 2 and SiO 2Al 2O 3. It was found that homologation of ethane to propane occurs via (1) dehydrogenation of ethane to ethylene, (2) homologation of ethylene to propylene, and (3) hydrogenation of propylene to propane. The rate-determining step was found to be hydrogenation of adsorbed propylene or that of adsorbed C 2H 5 species with an activation energy of 10.7 kcal/mole. In addition to homologation products, significant amounts of hydrogenolysis and dehydrogenation reaction products were also found. Dehydrogenation of ethane to ethylene had an activation energy of 25 kcal/mole, and it was quite similar to that for desorption of ethylene. Consequently, the dehydrogenation rate was assumed to be controlled by desorption of ethylene formed.

A study of oxygen self-diffusion in tile c-direction of rutile using a a nuclear technique : D.J. Derry, J.M. Calvert and D.G. Lees, Mettalurgy Department, the University, Manchester, M13 9PL, U.K. and Physics Department, The University, Manchester, M13 9PL, U.K.

Investigation of the Cs–Ba–Mo–O system by fused salt electrolysis at 960°C has led to the new related-hollandite compound Ba∼8/7Mo8O16. Single-crystals of Ba∼8/7Mo8O16 were examined by electron diffraction and high-resolution electron microscopy. Ba∼8/7Mo8O16 was found to present a tetragonal I basic unit-cell (a=10.21 Å, c=2.89 Å) with a one-dimensional modulation of wavevector q close to 4/7 along c* at room temperature. Refinement of the crystal structure was made on X-ray single crystal data in the seven-fold supercell in the three-dimensional space group I4 (a=10.214(2) Å, c=20.255(5) Å, Rw(F2)=0.0844 for all 7767 independent reflections and 149 parameters). In the latter supercell approach, the Mo atoms in the double edge-sharing rutile-type chains form Mo3 triangles and planar rhomboidal Mo4 clusters that coexist in equal proportions. The Mo–Mo distances vary from 2.5341(8) to 2.696(2) Å and from 2.5341(8) to 2.894(4) Å in the Mo3 and Mo4 clusters, respectively. The shortest intercluster distance is 3.047(4) Å. The Mo–O distances range between 1.81(1) to 2.418(8) Å as usually observed in reduced molybdenum oxides. The Ba2+ cations occupy the large square channels in square prismatic environment of oxygen atoms with the distribution sequence …Ba–□–Ba–Ba–□Ba–□–….

Structure and activity of tellurium-molybdenum oxide acrylonitrile catalysts

Ammoxidation of propylene to acrylonitrile (ACN) was investigated using various (Te, Mo)O catalysts at temperatures from 360 to 460 °C. Binary oxides are significantly more active than the component oxides and show a completely different product distribution. The reaction leads mainly to ACN and acrolein (80–90%, in varying ratios) and to CH 3CN (3%); the balance accounts for total oxidation products. The active phase is Te 2MoO 7, which acts through activation of the hydrocarbon at Te sites and insertion of oxygen at Mo sites. Site isolation in the active phase accounts for the high selectivity to ACN. The allotriomorphic texture of Te 2MoO 7 rationalizes variations in catalytic activity of the TeO 2MoO 3 system as a function of the composition. Decay of the catalysts by depletion of lattice oxygen was studied. Reactivation of a deactivated catalyst can be effected, but in nonequilibrium conditions transport phenomena lead to a migration of the degradation products, TeMo 5O 16, Te, and reduced molybdenum oxides. The primary function of cerium in an industrial (Ce, Mo, Te)O ammoxidation catalyst is its capacity to reoxidize its partners more readily as compared to a (Te, Mo)O solid.

Preparation of high surface area reduced molybdenum oxide catalysts

High surface area molybdenum oxides have been prepared by the thermal decomposition and reduction of molybdenum (VI) oxalate. It has been found that the initial trioxide formed is highly oxygen deficient and that the composition depends on the method of preparation, varying from MoO2.98, for an oxide prepared by decomposing the oxalate in nitrogen, to MoO2.82 for an oxide prepared in vacuum. The rate of reduction was found to be dependent on: the method used to decompose the oxalate; the temperature of the decomposition; the partial pressure of hydrogen; and the partial pressure of water vapour. Vacuum-prepared trioxides are reduced in a single stage to MoO2–x. Nitrogen-prepared trioxides reduce first to Mo4O11 or Mo2O5 depending respectively on whether “wet” or “dry” conditions are used. In most cases the reduction-time curves are essentially sigmoidal in character. Possible reduction mechanisms and rate-determining steps are discussed.

Structural characterisation of high surface area reduced molybdenum oxide catalysts

High surface area reduced molybdenum oxides have been prepared by the thermal decomposition and reduction of molybdenum (VI) oxalate. Nitrogen physisorption isotherms, analysed by the αs-method, have been used to determine the physical structure of the oxides. The effect of temperature, water vapour pressure and the degree of reduction, on the physical structure of the oxides has been studied. It is found that reduction creates initially slit-shaped micropores, which on further reduction, or in the presence of water vapour, broaden into mesopores. The changes in structure which accompany the passivation or the annealing of reduced oxides are described.

Superoxide ion formation process on reduced MoO 3TiO 2

Two novel Mo 5+ ions, different from either the D 2d symmetry Mo 5+ on anatase or the D 2hMo 5+ on rutile, appeared on partially reduced molybdenum oxide supported on α-titanic acid. The oxygen molecule is held on one of these novel Mo 5+ ions but is not reduced to the superoxide ion. Oxygen is reduced to O − 2 entirely by the Mo 4+ ion formed from the D 2d symmetry ion and the O − 2 is subsequently stabilized after moving to a Ti 4+-site.

Reduced molybdenum oxide catalysts with high surface areas. Preparation and activites

From solutions of ammonium molybdate this salt was precipitated with acetone. Decomposition in air at 330 °C yields MoO3 with a specific surface area of 17 m2/g, by means of reduction with hydrogen 4.5, 4 and 3.5 valent oxides may be formed with 30, 50 and 80 m2/g, respectively. Molybdenum (VI) oxide present as a monomolecular layer on supports is much less readily reduced than unsupported MoO3. This difference reflects the interaction of Mo ions with ions of the support. The reducibilities of the various catalysts show that Mo(VI) oxides interact far less with SiO2 than with Al2O3, CeO2 and ZrO2. This is also reflected in the rates of 2-propanol decomposition on these catalysts, the activities on MoOx and on MoOx−SiO2 being much higher than on the other catalysts.

The low-temperature catalytic oxidation of CO with N 2O by molybdenum oxide supported on silica gel

On the surface of partially reduced molybdenum oxide supported on silica gel the O − ion was formed from adsorbed N 2O and reacted with CO to give the CO 2 − ion. The latter ion was thermally stable to temperatures in excess of 100 °C. Preadsorption of CO inhibited the formation of the O − and CO 2 − ions, but the preadsorption of CO 2 had no effect on the formation of the two species. The supported molybdenum oxide was active for the oxidation of CO to CO 2 at temperatures as low as 0 °C. At all pressures and temperatures studied, the reaction rate was zero order in the partial pressure of CO and CO 2; whereas, the rate was zero or first order with respect to the N 2O partial pressure, depending upon the pressure and temperature. Apparent activation energies of 14.9 and 10.8 kcal/mole were determined for the zero and first order reactions, respectively. In view of the thermal stability of CO 2 − and the inhibiting effect of CO, it is concluded that the O − ion is not an intermediate in the low-temperature reaction. Rather, the reaction appears to involve molecular complexes of N 2O and CO on clusters of metal ions.

EPR evidence for 17O − on molybdenum oxide supported by silica-gel

The EPR spectrum of 17O − on partially reduced molybdenum oxide supported on silica-gel has been observed following adsorption of N 2O at room temperature. The spectrum is chracterized by g ⊥=2.019 and g |=2.002 with a | 17O −=96±1 G and a | 95MO, 97MO=7.5±0.5 G. The O −ion appears to undergo exchange with oxide ions at the surface.

Disproportionation of Propylene over Supported Metal Oxide Catalysts

Disproportionation of propylene on several metal oxide catalysts was studied by means of a flow method. The effects of pretreatment of catalyst with various gases and of various supports on the reaction were investigated in order to clearify the formation of active centers of catalyst. The reaction was carried out at the temperature range from 100°C to 200°C on each catalyst activated 'previously with dry nitrogen gas, dry oxygen or dry hydrogen at 500°C.It was found that WO3-γ-Al2O3 was the most active catalyst for this reaction, but selectivity was rather small. On the other hand, the activity of MoO8-γ-Al2O3 was very high at the beginning of the reaction, but the activity decreased gradually with the reaction time. When the catalyst was pretreated with nitrogen, the activity was greatly different with the various supports, that is, MoO3-SiO2.Al2O3 was most active, and both MoO2-SiO, and MoO3-α-Al2O3 had no activity for this reaction. From these results, it seems that the activity of several supported MoO3 was correlated with the acidity of these carriers.By reducing all these catalysts with hydrogen before the reaction, the activity prominently increased, especially the activity of both MoO3-SiO2 and MoO3-α-Al2O3 became almost equivalent to that of MoO3-γ-Al2O3.From these phenomena, it is concluded that the active center of these catalyst is slightly reduced molybdenum oxide, and the acidic carrier plays a role in forming the active center during the pretreatment of catalyst, without directly participating in the reaction.