Enhanced sulfur‐resistant methanation performance over MoO3–ZrO2 catalyst prepared by solution combustion method

Sulfur‐resistant methanation of syngas was studied over MoO₃–ZrO₂ catalysts at 400°C. The MoO₃–ZrO₂ solid‐solution catalysts were prepared using the solution combustion method by varying MoO₃ content and temperature. The 15MoO₃–ZrO₂ catalyst achieved the highest methanation performance with CO conversion up to 80% at 400°C. The structure of ZrO₂ and dispersed MoO₃ species was characterized using X‐ray diffraction and transmission electron microscopy. The energy‐dispersive spectrum of the 15MoO₃–ZrO₂ catalyst showed that the solution combustion method gave well‐dispersed MoO₃ particles on the surface of ZrO₂. The structure of the catalysts depends on the Mo surface density. It was observed that in the 15MoO₃–ZrO₂ catalyst the Mo surface density of 4.2 Mo atoms nm^?2 approaches the theoretical monolayer capacity of 5 Mo atoms nm^?2. The addition of a small amount of MoO₃ to ZrO₂ led to higher tetragonal content of ZrO₂ along with a reduction of particle size. This leads to an efficient catalyst for the low‐temperature CO methanation process.     

Fabrication of newly developed pectin –GeO2 nanocomposite using extreme biomimetics route and its antibacterial activities

The combination of pectins and germanium dioxide may generate novel materials with excellent and unique properties combining the advantages of macromolecules, derived from renewable resources and metal oxide nanoparticles. Pectin–GeO₂ nanocomposite was prepared by hydrothermal method at room temperature. Structural morphology and chemical interactions between GeO₂ and pectin were analyzed using Fourier Transform Infrared Spectroscopy Equipped with Attenuated Total Reflectance (FTIR-ATR), AC impedance spectroscopy, Scanning Electron Microscopy-Energy Dispersive X-ray Spectrophotometer (SEM-EDS) Thermo gravimetric analysis (TG) and Differential Scanning Calorimetry (DSC). According to the TEM observation, the average composite granules size was about 70 nm and the embedded GeO₂ nanoparticles were uniform with an average diameter of 20 nm. The pectin-germanium dioxide degradation was observed in one single DSC endoderm peak at 100°C (Area swept 276.4 mJ and enthalpy change 48.1 J/g) and three DTG peaks in the temperature range between 165 and 570°C. All the results suggest the pectin–GeO₂ nanocomposite as a promising candidate for biomedical and environmental applications.     

Die relative Unterkühlung an Quarzglasoberflächen und anderen Substraten beim chemischen Transport fester Stoffe über die Gasphase

The Relative Undercooling on Silica Glass Surfaces and other Substrates during the Chemical Transport of Solids via the Vapor-phase . The relative undercooling on etched surfaces of silica glass at the chemical transport of ZnS in a stream of gaseous iodine at 652–854°C is found to be ΔT = 37–43°. Scrapers on silica glass lead to a substantial smaller undercooling. During the deposition of ZnS (made from “pure” components) in a temperature gradient one finds a remarkable fractionation. In closed (etched) silica glass ampoules the relative undercooling is determined for the systems ZnS/I₂, ZnSe/I₂, ZnS/HCl; ZnS/H₂, CdS/I₂, CdSe/I₂, Al₂S₃/I₂ and Nb₂O₅/NbCl₅ using a special furnace, The region free of nuclei (or crystals) for instance at T₂ ≈ 800°C depending on the system (and T₂) is ΔT ≈ 13–45°. The variation of the substrates showed: for fire polished silica surfaces for ZnS/I₂ is ΔT ≈ 56°; for the different quartz-faces and ZnS/I₂ is ΔT ≈ 13–35°. Generally, on different substrates (broken pieces, fragments) one finds for ZnS/I₂ ΔT ≈ 20–28°. Using another way for the systems MoO₃/Cl₂, MoO₃/Cl₂, Ar, MoO₃/Cl₂, O₂ and MoO₃/HgCl₂ with T₂ a strongly decreasing value of ΔT is found.     

Das Phasendiagramm des Systems TeO2–MoO3

Phase Diagram of the System TeO₂? MoO₃ The phase equilibrium diagram of the system TeO₂? MoO₃ has been studied using differential thermal analysis. It is shown that a new congruently melting phase, Te₂MoO₇, is formed (m. p. 551°C). The eutectics were found at 526°C near 55.5 mole% TeO₂ and at 543%C near 67.5 mole% TeO₂. The compound Te₂MoO₇ shows glass-forming tendency.     

Ag9I(GeO4)2 – Containing Two‐dimensionally Linked [IAg12] Metallo Complexes

Ag₉I(GeO₄)₂ was obtained for the first time by reacting a stoichiometric mixture of Ag₂O, AgI, and GeO₂, at elevated oxygen pressures, adding a small portion of distilled water. The synthesis was done at 480 °C and 110 MPa of oxygen pressure. It crystallizes in space group C2/m, with the unit cell dimensions a = 17.3736(9) Å, b = 6.9177(4) Å, c = 5.7176(3) Å, β = 105.501(3)°, V = 662.18(6) ų, and Z = 2. The structure refinement was based on 638 independent reflections and resulted in R₁ = 6.26 %. The crystal structure consists of isolated (GeO₄)^4– ions and [IAg₁₂] metallo complexes, the latter are interconnected through each two common edges and corners corresponding to [IAg_6/1Ag_6/2], thus forming infinite layers within the (100) plane. The Ag/I slabs are stacked perpendicular to the a‐axis with an interlayer distance of about 3.4 Å. The (GeO₄)^4– anions are located in the gaps between the silver iodide layers. According to the results of impedance measurements, Ag₉I(GeO₄)₂ is a good silver ion conductor. The compound shows an increase in the ionic conductivity in the temperature range of 30 to 310 °C, and has a silver ion conductivity of 1.1 × 10^–3 Ω^–1 cm^–1 at room temp. The activation energy for silver ion conduction is 0.35 eV, in the temperature range from 25 to 190 °C.     

Study on the formation process of MoO3/Fe2(MoO4)3 by mechanochemical synthesis and their catalytic performance in methanol to formaldehyde

Mechanochemical method has applied to the green preparation of iron-molybdenum catalyst efficiently, and their catalytic performance was evaluated by the oxidation of methanol to formaldehyde. In order to investigate the formation process of iron-molybdenum catalyst based on mechanochemical method, various characterization techniques have been employed. Results indicate that iron-molybdenum catalyst could not be generated during ball milling process without calcining, and calcination is crucial step to regulate the ratio of MoO₃ and Fe₂(MoO₄)₃. For the formation of MoO₃ and Fe₂(MoO₄)₃ phase, 180 °C could be the key turning temperature point. Fe₂(MoO₄)₃ and MoO₃ phases are concurrently emerged when Mo/Fe atomic ratio exceeds 1.5. The aggregation of Fe₂(MoO₄)₃ is severe with the increasing calcination temperature. Fe₂(MoO₄)₃ is stable below 600 °C, while MoO₃ phase could be subliming with the increasing temperature. The catalytic performance of iron-molybdenum catalyst has closely correlation with the phase compositions, which can be controlled by synthesis temperature and Mo/Fe molar ratio. The iron-molybdenum catalyst with Mo/Fe atomic ratio of 2.6 calcined at 500 °C for 4 h showed the best methanol conversion (100%) and formaldehyde yield (92.27%).

     

Synthesis,crystal structure,and electrical properties of the new ternary molybdate Rb<Subscript>5</Subscript>NdHf(MoO<Subscript>4</Subscript>)<Subscript>6</Subscript>

The subsolidus phase relations in the ternary salt system Rb₂MoO₄-Nd₂(MoO₄)₃-Hf(MoO₄)₂ were studied by X-ray powder diffraction. The ternary molybdates Rb₅NdHf(MoO₄)₆ (1) and Rb₂NdHf₂(MoO₄)_6.5 are formed in this system. Compound 1 without impurities was synthesized by the solid-phase method by varying the temperature in the range of 400–600 °C and the annealing time from 70 to 110 h. Single crystals of compound 1 were grown by the flux method. The structure of compound 1 was established and the electrical properties of ceramic samples of this compound were investigated. This ternary molybdate has mixed electronic-ionic conductivity with the ionic component predominating at 200–500 °C. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2063–2066, November, 2007.     

Solid solubility and cation distribution in the system Co2GeO4Mg2GeO4

In the system Co₂GeO₄Mg₂GeO₄, solid solubilities in spinel and olivine structures were studied on samples prepared by solid state reaction at temperatures of 1000–1300°C. The solubility limits were determined from the identification by X-ray powder pattern and the change of the lattice constant of spinel with composition. The relation between temperature and the free energy difference ΔG° which was estimated from the solubility limits agreed qualitatively with the fact that the spinel phase of Mg₂GeO₄ is stable at low temperatures under atmospheric pressure. The spinels were also synthesized at 800°C under the pressure of 20 kb. Over the whole range of composition, the cation distribution was found to be normal with u = 0.375. Above 1000°C under 20 kb in the presence of water, the spinels, except Co₂GeO₄, were found to react with water to form enstatite and probably magnesium hydroxide in an amorphous state.     

Growth of carbon nanotubes from butadiene on a Fe-Mo-Al2O3 catalyst

The MoO₃-Fe₂O₃-Al₂O₃ catalysts were prepared from metal nitrates using a coprecipitation method. It was found that the modification of an alumina-iron catalyst with molybdenum oxide resulted in the formation of a solid solution based on hematite, in which a portion of iron ions was replaced by aluminum and molybdenum ions. The MoO₃-Fe₂O₃-Al₂O₃ catalyst was reduced with a reaction mixture at 700°C. Under the action of 1,3-butadiene diluted with hydrogen, the solid solution based on hematite was initially converted into magnetite and then into an Fe-Mo alloy. The modification of an alumina-iron catalyst with molybdenum oxide considerably changed its properties in the course of carbon nanotube formation. As the Mo content was increased, the yield of carbon nanotubes passed through a maximum. The optimum catalyst was 6.5% MoO₃–55% Fe₂O₃-Al₂O₃. The addition of small amounts of MoO₃ (to 6.5 wt %) to the aluminairon catalyst increased the dispersity and modified the properties of active metal particles: because of the formation of an Fe-Mo alloy, the rate of growth decreased but the stability of carbon nanotube growth and the yield of the nanotubes increased. A further increase in the molybdenum content decreased the yield because molybdenum is inactive in the test process.     

The relative stabilities of Bi2MoO6 polymorphs

The relative stability of Bi₂Mo₆ polymorphs was studied by isothermal heating at 250–635°C, and 100–1500 kg/cm². The results obtained follow: (1) A reversible transition was observed between two stable phases at low (L) and high (H) temperatures, γ(L)-Bi₂MoO₆ with the koechlinite structure and γ(H)-Bi₂MoO₆ (=γ′ labeled by Elman). (2) A pressure-temperature phase diagram of Bi₂MoO₆ was drawn and it showed that the γ(L)-form was more stable than the γ(H)-form in the low-temperature and high-pressure region. (3) The transition temperature of γ(L) ? γ(H) under atmospheric pressure was estimated to be about 570°C by extrapolation of the phase boundary. (4) A third modification, γ″-Bi₂MoO₆ (a metastable phase), was not detected in the experiments. A free-energy-temperature diagram for the three modifications, γ(L), γ(H), and γ″, is proposed on the basis of the present experimental results and previously published data.     

Effect of γ-irradiation and doping with MoO3 and V2O5 on surface and catalytic properties of manganese oxides

The effects of γ-irradiation (0.2–1.6 MGy), thermal treatment and doping with MoO₃ and V₂O₅ (0.25–4 mol%) on the surface and catalytic properties of manganese oxides prepared by thermal decomposition of manganese carbonate at 400°C and 600°C have been investigated. The techniques employed were X-ray diffraction, nitrogen adsorption at −196°C, oxidation of CO by O₂ at 120–220°C and decomposition of H₂O₂ at 20–50°C. The results revealed that γ-irradiation decreased the particle size of manganese oxides, increased their specific surface areas, decreased the amount of surface excess oxygen and decreased their catalytic activities. The doping with MoO₃ and V₂O₅ conducted at 600°C brought about a measurable decrease in the BET-surface area and catalytic activities of the treated solids. These results were discussed in terms of splitting of manganese oxide particles and removal of chemisorbed oxygen by treating with γ-irradiation and formation of manganese molybdate and vanadates by treating with the used dopant oxides.     

Thermal Decompositions of Pure and Mixed Manganese Carbonate and Ammonium Molybdate Tetrahydrate

The thermal decompositions of pure and mixed manganese carbonate and ammonium molybdate tetrahydrate in molar ratios of 3:1, 1:1 and1:3 were studied by DTA and TG techniques. The prepared mixed solid samples were calcined in air at 500, 750 or 1000°C and then investigated by means of an XRD technique. The results revealed that manganese carbonate decomposed in the range 300–1000°C, within termediate formation of MnO₂, Mn₂O₃ andMn₃O₄. Ammonium molybdate tetrahydrate first lost its water of crystallization on heating, and then decomposed, yielding water and ammonia. At 340°C,MoO₃ was the final product, which melts at 790°C. The thermal treatment of the mixed solids at 500, 750 or 1000°C led to solid-solid interactions between the produced oxides, with the formation of manganese molybdate. At 1000°C, Mn₂O₃ and MoO₃ were detected, due to the mutual stabilization effect of these oxides at this temperature. This revised version was published online in July 2006 with corrections to the Cover Date.     

Thermodynamic relations among olivine,spinel, and phenacite structures in silicates and germanates: I. Volume relations and the systems NiOMgOGeO2 and CoOMgOGeO2

An experimental approach is outlined to systematically obtain free energy differences among olivine, spinel, and phenacite forms of silicates and germanates from the thermodynamics of terminal solid solutions in ternary systems. This is applied to the ternary systems NiOMgOGeO₂ and CoOMgOGeO₂ at 1200°C in air and to the system NiOMgOGeO₂ at 800°C and 0.57 kbar water pressure. From the location of conjugation lines, activity-composition relations along each orthogermanate join are calculated. The free energies of transformation from the olivine to the spinel structure at 1200°C are estimated to be +1.6, ?3.5, and ?8.2 kcal/mole for Mg₂GeO₄, Co₂GeO₄, and Ni₂GeO₄, respectively.Volume changes for the spinel-olivine and olivine-phenacite transitions are estimated for the silicates and germanates of Mg, Mn, Fe, Co, Ni, and Zn.     

Syntheses,spectroscopic, and magnetic properties of polystyrene-anchored coordination compounds of tridentate ONO donor Schiff base

The crosslinked chloromethylated polystyrene (PSCH₂–Cl) reacts with the Schiff base, derived from condensation of PSCH₂–Cl with 3-formylsalicylic acid and salicylhydrazide to form a polystyrene-anchored Schiff base, PSCH₂–LH₃ (1). Compound 1 reacts with a number of metal ions to form polystyrene-anchored coordination compounds, PSCH₂–LHM?·?DMF (where M?=?Cu, Zn, Cd, UO₂, and MoO₂), PSCH₂–LHM′?·?3DMF (where M′?=?Mn, Co, and Ni), PSCH₂–LHFeCl?·?2DMF, and PSCH₂–LHZr(OH)₂?·?2DMF. The polystyrene-anchored coordination compounds have been characterized by elemental analyses, spectra (infrared, reflectance, and electron spin resonance) and magnetic susceptibility measurements. The polystyrene-anchored compounds are magnetically dilute. Shifts in band positions of the groups involved in coordination have been utilized to find tridentate ONO donor behavior of 1. The polystyrene-anchored Zn(II), Cd(II), Zr(IV), MoO₂(VI), and UO₂(VI) compounds are diamagnetic, while Mn(II), Co(II), Ni(II), Cu(II), and Fe(III) compounds are paramagnetic. The polystyrene-anchored Cu(II) compound is square planar; Zn(II) and Cd(II) compounds are tetrahedral; Co(II), Ni(II), Mn(II), Fe(III), MoO₂(VI), and UO₂(VI) compounds are octahedral; and Zr(IV) compound is pentagonal bipyramidal.     

A new phase in the MnII–SeIV–MoVI–O system,Mn(MoO3)(SeO3)(H2O): Hydrothermal synthesis,crystal structure and properties

A new phase in the Mn^II–Se^IV–Mo^VI–O system, Mn(MoO₃)(SeO₃)(H₂O) (1), has been hydrothermally synthesized with a high yield (82%), and characterized by IR, TG-DSC, magnetism measurement and single crystal X-ray diffraction. The structure of Mn(MoO₃)(SeO₃)(H₂O) features a complicated 3D network composed of the 1D molybdenum(VI) oxide chains and the 1D manganese(II) selenite chains interconnected via Se–O–Mo and Mn–O–Mo bridges. It is stable up to approximately 340 °C, and losses water molecule at 340 °C, then release SeO₂ at about 420 °C. The result of magnetic property measurements has indicated that there exist antiferromagnetic interactions between Mn(II) centers. Photocatalysis experimental result illustrates that the compound exhibits good photocatalytic performance for degradation of RhB under visible light irradiation.     

A new reduction route for the synthesis of nanoscale metals and metal oxides with ascorbic acid at low temperature

Reduction of the transition metal complexes in aqueous solution has been investigated systematically by ascorbic acid as the reducing agent without the assistance of any surfactant. Nanoparticles of α-Mn₂O₃, Ag and Cu were synthesized directly through aqueous phase reduction at room temperature. Nanoscale metal oxides such as Co₃O₄, α-Fe₂O₃ and MoO₂ were obtained through ascorbic acid reduction in alkali medium at 40°C. All the products were characterized on their structure and micro-morphology by the X-ray diffraction (XRD) and atomic force microscopy (AFM). The particle size of metal and metal oxides was about 10–50 nm. The reaction details and features were described and discussed.     

Thermal and X-ray diffraction studies of the solid–solid interactions in CuO–MoO3/MgO system

The solid–solid interactions in pure and MoO₃-doped CuO/MgO system were investigated using TG, DTA and XRD. The composition of pure mixed solids were 0.1CuO/MgO, 0.2CuO/MgO and 0.3CuO/MgO and the concentrations of MoO₃ were 2.5 and 5 mol%. These solids were prepared by wet impregnation of finely powdered basic magnesium carbonate with solutions containing calculated amounts of copper nitrate and ammonium molybdate followed by heating at 400–1000°C. The results revealed that ammonium molybdate doping of the system investigated enhanced the thermal decomposition of copper nitrate and magnesium hydroxide which decomposed at temperatures lower than those observed in case of the undoped mixed solids by 70 and 100°C, respectively. A portion of CuO present dissolved in the lattice of MgO forming CuO–MgO solid solution with subsequent limited increase in its lattice parameter. The other portion interacted readily with a portion of MoO₃ at temperatures starting from 400°C yielding CuMoO₄ which remained stable up to 1000°C. The other portion of MoO₃ interacted with MgO producing MgMoO₄ at temperatures starting from 400°C and remained also stable at 1000°C. The diffraction peaks of Cu₂MgO₃ phase were detected in the diffractograms of pure and MoO₃-doped 0.3CuO/MgO precalcined at 1000°C. The formation of this phase was accompanied by an endothermic peak at 930°C.     

Na4SeO5, ein neues Pentaoxoselenat(VI) – Synthese,Charakterisierung und Vergleich mit isotypem Na4MoO5

Na₄SeO₅, a Novel Pentaoxoselenate(VI) – Synthesis, Charakterisation, and Comparison with Na₄MoO₅ Na₄SeO₅ was prepared by high pressure solid state reaction at 500 °C and at a hydrostatic pressure of 2.5 Gpa from a mixture of Na₂O and Na₂SeO₄ in silver crucibles and Na₄MoO₅ by solid state reaction at 450 °C from a mixture of Na₂O and MoO₃. The crystal structures of both new compounds were solved and refined using X‐ray powder methods (Profilematching Na₄SeO₅: P1, a = 988.3(1), b = 988.4(1), c = 558.6(1) pm, α = 96.25(1)°, β = 96.24(1)°, γ = 113.41(1)°, R_p = 0.0783, R_wp = 0.1037. Profilematching Na₄MoO₅: P1, a = 999.5(1), b = 1002.0(1), c = 565.1(1) pm, α = 96.54(1)°, β = 96.29(1)°, γ = 113.35(1)°, R_p = 0.0623, R_wp = 0.0867). Both compounds contain novel XO₅^4– anions of approximately tetragonal pyramidal shape. The crystal structures are consistent with spectroscopic data (IR, Raman).     

A new ferroelastic transition in some A2(MO4)3 molybdates and tungstates

We have found for the first time a ferroelastic transition in many molybdates and tungstates with the Sc₂(MoO₄)₃-type structure. Below the transition these phases are monoclinic ($\text{P2}{}_1\text{a}$), and above the transition they are orthorhombic (Pnca). Observed transition temperatures are: Al₂(MoO₄)₃, 200°C; Al₂(WO₄)₃, ?6°C; Cr₂(MoO₄)₃, 385°C; Fe₂(MoO₄)₃, 499°C; In₂(MoO₄)₃, 335°C; In₂(WO₄)₃, 252°C; and Sc₂(MoO₄)₃, 9°C.     

Excellent Electrochemical Properties of Yolk–Shell MoO3 Microspheres Formed by Combustion of Molybdenum Oxide–Carbon Composite Microspheres

Yolk–shell MoO₃ microspheres are prepared by a two‐step process in which molybdenum oxide–carbon (MoO_x–C) composite microspheres are first obtained by spray pyrolysis, followed by combustion at 400 °C in air. The yolk–shell microspheres exhibit excellent electrochemical properties and structural stability.