Promotion effects of alkali metals on iron molybdate catalysts for CO_(2)catalytic hydrogenation

CO_(2)hydrogenation is an attractive way to store and utilize carbon dioxide generated by industrial processes,as well as to produce valuable chemicals from renewable and abundant resources.Iron catalysts are commonly used for the hydrogenation of carbon oxides to hydrocarbons.Iron-molybdenum catalysts have found numerous applications in catalysis,but have been never evaluated in the CO_(2)hydrogenation.In this work,the structural properties of iron-molybdenum catalysts without and with a promoting alkali metal(Li,Na,K,Rb,or Cs)were characterized using X-ray diffraction,hydrogen temperatureprogrammed reduction,CO_(2)temperature-programmed desorption,in-situ^(57)Fe Mossbauer spectroscopy and operando X-ray adsorption spectroscopy.Their catalytic performance was evaluated in the CO_(2)hydrogenation.During the reaction conditions,the catalysts undergo the formation of an iron(Ⅱ)molybdate structure,accompanied by a partial reduction of molybdenum and carbidization of iron.The rate of CO_(2)conversion and product selectivity strongly depend on the promoting alkali metals,and electronegativity was identified as an important factor affecting the catalytic performance.Higher CO_(2)conversion rates were observed with the promoters having higher electronegativity,while low electronegativity of alkali metals favors higher light olefin selectivity.

Synthesis and Crystal Structure of a Polyoxomolybdate Framework Modified by Mn-L Units(L=3-(2-Pyridyl)pyrazole)

A new polyoxomolybdate compound,namely {[MnII（L）（4,4？-Hbipy）（H2O）2]2 [Mo5O15（PO4）2]}.2H2O 1（L = 3-（2-pyridyl）pyrazole,4,4＇-Hbipy = protonated 4,4＇-bipyridine）,was designed and synthesized under hydrothermal conditions.Single-crystal X-ray diffraction analysis result reveals that the [Mo5O15（PO4）2]6-cluster in compound 1 links to two MnII cations via the oxygen of PO43-,which is further coordinated by one 3-（2-pyridyl）pyrazole,one 4,4＇-Hbipyridine,and two water molecules.

Synthesis and Structural Characterization of a Polyoxomolybdate HNa_7[Mo_(36)O_(112)(H_2O)_(16)]·47H_2O

A new polyoxomolybdate complex HNaT[Mo36O112（H2O）16]·47H2O 1 has been prepared in the beaker solution and characterized by single-crystal X-ray diffraction and elemental analyses. Crystal data： H127Mo36Na7O175, Mr = 6542.79, monoclinic, C2/c, a = 40.891（6）, b = 17.900（3）, c = 25.580（4）A, β = 125.673（2）°, V = 15210（4）A3, Z = 4, Dc = 2.857 g/cm^3, F（000） = 12464,μ = 3.013 mm^-1, R = 0.0633 and wR = 0.1654 （I 〉 20（I））. With the bridging sodium cations, the [Mo36Ou2（H2O）16]^8- units in compound 1 are linked to form a one-dimensional structure, on the basis of which a three-dimensional architecture is further constructed via other sodium cations and complicated hydrogen bonds.

Syntheses and Crystal Structures of Two Octamolybdate Compounds Modified by Cu~Ⅱ-Imidazole Cations

Two new polyoxomolybdate compounds,namely（CuIIL2）2[CuⅡ（HL）2]2[Mo8O26（HL）2].（H2O）4（1） and [CuⅡ（HL）2]2[β-Mo8O26]（HL）2（2）（HL=imidazole）,were designed and synthesized under hydrothermal conditions.X-ray diffraction analyses reveal that compound 1 consists of one Mo8O26（HL）24-cluster,two CuL2,two Cu（HL）22＋,and four disassociated water molecules;and compound 2 is constructed by one β-Mo8O264-cluster,two Cu（HL）22＋,and two uncoordinated imidazole molecules.

Hydrothermal Syntheses and Structural Characterizations of Two ML-Containing Polyoxomolybdates：[Cu^Ⅱ2（HL）3]2[Mo8O26）]·（H2O）4 and [Ni^Ⅱ（HL）3]2（Mo8O26）·（H2O）3（HL=3-（2-Pyridyl）pyrazole）

Two new polyoxomolybdate compounds,namely CuII2（HL）3]2[Mo8O26]·（H2O）4（1） and [NiII（HL）3]2（Mo8O26）·（H2O）3（2）（HL = 3-（2-pyridyl）pyrazole）,were designed and synthesized under hydrothermal conditions.X-ray diffraction analyses reveal that compound 1 consists of one β-Mo8O264-cluster and a Cu2 dimer which is built from two Cu（II） ions linked by three 3-（2-pyridyl）pyrazole ligands.Compound 2 is generated by two kinds of polyoxomolybdate clusters of α-[Mo8O26]4-and β-[Mo8O26]4-.In complexes 1 and 2,the multi-dimensional frameworks are con-structed with the help of hydrogen-bonding links between the terminaloxygen atoms of [Mo8O26]4-,water molecules,and 3-（2-pyridyl）pyrazole ligands.Crystal data of 1：C24H25Cu2Mo4N9O15,Mr = 1190.37,monoclinic,space group P21/c,a = 10.850（2）,b = 18.510（4）,c = 17.230（3） ,β = 100.57（3）°,V = 3401.6（12） 3,Z = 4,Dc = 2.324 g/cm3,F（000） = 2312,μ = 2.742 mm-1,R = 0.0302 and wR = 0.0775（Ⅰ 〉 2σ（Ⅰ））;Crystal data for 2：C48H48Mo8N18Ni2O29,Mr = 2225.98,monoclinic,space group P21/n,a = 20.799（2）,b = 14.7970（13）,c = 23.141（2） ,β = 91.6180（10）°,V = 7119.0（11） 3,Z = 4,Dc = 2.077 g/cm3,F（000） = 4344,μ = 1.968 mm-1,R = 0.0309 and wR = 0.0696（Ⅰ〉 2σ（Ⅰ））.

Synergistic Corrosion Inhibition Effect of Molybdate and Phosphate Ions for Anodic Oxidation Film Formed on 2024 Aluminum Alloy

In order to effectively improve the corrosion resistance of aluminum alloys, anodic oxidation technique was used to generate the oxide film. We investigated the influences of two inorganic corrosion inhibitors(ammonium dihydrogen phosphate and sodium molybdate) on the corrosion resistance of anodic oxidation films on 2024 aluminum alloy, and studied the synergistic effect of two corrosion inhibitors. The corrosion resistance of anodic oxidation film in 3.5 wt% NaCl solution was evaluated by electrochemical impedance spectroscopy(EIS) and potentiodynamic polarization curves. Results show that, after adding the single ammonium dihydrogen phosphate or sodium molybdate of 0.01 M to oxalic acid electrolyte, inhibition efficiencies of the anodized samples are 10% and 47%, respectively. However, in the presence of two inhibitors with the same concentration of 0.01 M, inhibition efficiency can be as high as 92%. Therefore, we observed the significantly synergistic corrosion inhibition effect of molybdate and phosphate ions for anodic oxidation film formed on 2024 aluminum alloy.

Luminescent Properties of Samarium Ion in Calcium Molybdate

Trivalent samarium ion (Sm^(3+)) activated calcium molybdate (CaMoO_4) phosphor was prepared by solid-state reaction in air. The XRD pattern of the powder CaMoO_4∶Sm shows that the CaMoO_4∶Sm single phase is developed fully through our preparation procedure. The excitation spectrum of CaMoO_4∶Sm is composed of a broad absorption of host and some sharp lines of the f-f transition absorption of Sm^(3+). Illustrated in photoluminescence spectrum, CaMoO_4 doped with Sm^(3+) displays orange red emission that is ascribed to the inner 4f^5 electron transitions ~6H_(7/2)(orange)and ~6H_(9/2)(red)of Sm^(3+). Different from the sites of Sm^(3+) in CdWO_4, the Sm^(3+) ions substitute for the Ca^(2+) and form only one type emission center in the CaMoO_4 crystal lattice.

Synthesis and Structure Investigation of a Transition Metal Ion Bridging Bis(diphosphopentamolybdates),[H_2BIIM]_3[HBIIM]_4[Mn(H_2O)_4(P_2Mo_5O_(23))_2]·7H_2O

A novel transition metal ion bridging bis（diphosphopentamolybdates） has been synthesized and characterized by elemental analysis,IR spectrum,UV spectrum and single-crystal X-ray diffraction.The single-crystal structure analysis shows that the compound consists of seven charge-compensating 2,2＇-biimidazole cations （BIIM=2,2＇-biimidazole） and one dumbbell-like [Mn（H2O）4（P2Mo5O23）2]10-heteropolyanion which is constructed by two [P2Mo5O23]6-clusters bridged through one [Mn（H2O）4]2＋ cation.

Synthesis and Properties of Eu_(3+) Activated Strontium Molybdate Phosphor

In order to prepare fluorescent material for white Light Emitting Diodes （LEDs）, a new Eu^3＋ activated molybdate phosphor SrMoO4 was fabricated with solid-state method. X-ray diffraction （XRD） showed that the doping of trivalent europium ion reduced the lattice parameters. The excitation and emission spectra indicated that this phosphor could be excited effectively by the visible light, and then emitted red light with the peaks located at 616 and 624 nm. The influence of Eu^3＋ concentration on the luminescent properties of Eu^3＋ doped SrMoO4 was investigated and the 25% （mole fraction） was the appropriate molar concentration. The reaction time and temperature had obvious effect on the luminescent properties. The luminescent intensity reached the strongest when it was sintered at 800 ℃ for 3 h.

Enhancing the Stability of Passive Film on 304 SS by Chemical Modification in Alkaline Phosphate–Molybdate Solutions

The purpose of this work was to enhance the corrosion resistance of the passive fi lm on 304 stainless steel(SS)by chemical modifi cation in alkaline phosphate–molybdate solutions.The 304 SS was passivated in both phosphate and phosphate–molybdate mixed solutions to investigate the eff ect of molybdate on its corrosion resistance.The experimental results indicated that the passive fi lm showed better corrosion resistance in Cl?-containing solutions after modifi cation in phosphate–molybdate solutions than in phosphate-only solutions.Energy-dispersive spectroscopy analyses revealed that the passive fi lm formed in phosphate–molybdate solutions contained Mo and P after modifi cation,which is the reason for the enhanced corrosion resistance.

Role and Mechanism of Action of Exogenous Salicylic Acid and Sodium Molybdate in Improving Cold Tolerance of Bougainvillea glabra

This study was conducted to comprehensively evaluate the effects of salicylic acid and sodium molybdate on cold tolerance of an ornamental plant Bougainvillea glabra and to provide a theoretical guidance for landscape maintenance.B.glabra plants were treated with 0.5 mmol/L salicylic acid and 2.0 μmol/L alone or in combination,and then exposed to low temperature stress before physiological indices were measured.The results showed that all salicylic acid and sodium molybdate treatments reduced the relative conductivity and malondialdehyde( MDA) content of B.glabra to varying extents under the stress of low temperature,and more significant effect was achieved by using the two agents in combination.Oxygen free radicals production rate increased with decreasing temperature from 20 to 6 ℃,but declined with temperature decreasing from 3 to-3 ℃.The SOD activity of the control( CK) was significantly lower than that of other treatments at 0 and-3 ℃.The treatments with salicylic acid and sodium molybdate alone and in combination increased POD activity of B.glabra plants,especially at 0 ℃,as the POD activity of treatments T1,T2 and T3 was significantly higher than that of CK at 0 ℃.In addition,under low temperature stress,the contents of soluble sugar,starch and proline increased initially and decreased subsequently with temperature decreasing.The soluble sugar content at 3 ℃,starch and proline contents at 0 and-3 ℃ in treatments with salicylic acid and sodium molybdate alone and in combination were significantly higher than those of CK.All above results proved that salicylic acid and sodium molybdate are able to improve cold tolerance of B.glabra,and better effect can be achieved by using them together.

Preparations of Pure Alkaline Earth Molybdate Phases from Single Molecular Precursors

The pure phases of alkaline earth molybdates MMoO 4, where M=Mg, Ca, Sr or Ba, were synthesized via the calcination of the related citrato oxomolybdate complexes. The mixed metal oxides can be highly dispersed at the atomic level due to the existence of uniform citrato oxomolybdenum precursors in definite composition. The complexing effect helps to produce the fine-grained oxides with particle size in the ultrafine scale(<100 nm) at heat-treatment temperatures below 500 ℃. The structures of the precursor complexes and the finally heat-treated particles were studied by means of IR, XRD, DSC, DTA and TG techniques. The morphologies of the particles were observed by using the SEM technique. The average particle sizes were calculated to be in the range of 30_50 nm based on X-ray diffraction line-broadening and SEM images, indicating the poor conglomeration of crystallite at low temperatures.

Effects of iron precursors on the structure and catalytic performance of iron molybdate prepared by mechanochemical route for methanol to formaldehyde

Mechanochemical synthesis has been applied for many novel material preparations and gained more and more attention due to green and high-efficiency recently. In order to explore the influences of iron precursors on structure and performance of iron molybdate catalyst prepared by mechanochemical route, three typical and cheap iron precursors have been used in preparation of iron molybdate catalyst. Many characterization methods have been employed to obtain the physical and chemical properties of iron molybdate catalyst. Results indicate that iron precursors have the significant impact on the phase composition, crystal morphology and catalytic performance in the conversion of methanol to formaldehyde. It is hard to regulate the phase composition by changing Mo/Fe mole ratios for Fe2(SO4)3 as iron precursor. In addition, as for Fe2(SO4)3, the formaldehyde yield is lower than that from iron molybdate catalyst prepared with Fe(NO3)3·9H2O due to the reduction in Fe2(MoO4)3 phase as active phase. Based on mechanochemical and coprecipitation method, the solvent water could be a key factor for the formation of MoO3 and Fe2(MoO4) for FeCl3·6H2O and Fe2(SO4)3 as precursors. Iron molybdate catalyst prepared with Fe(NO3)3·9H2O by mechanochemical route, shows the best methanol conversion and formaldehyde yield in this reaction.

Characterization and photoluminescence properties of ultrafine copper molybdate(α-CuMoO_4) powders prepared via a combustion-like process

We report a simple method for preparing copper（II） molybdate（CuMoO_4） powders via a combustion-like process. A gel was first prepared by the polymerizable complex method, where citric acid was used as a complexing and polymerizing agent and nitric acid was used as an oxidizing agent. The thermal decomposition behavior of the（CuMo）-precursor gel was studied by thermogravimetry–differential thermal analysis（TG–DTA）, Fourier transform infrared spectroscopy（FTIR）, and X-ray diffraction（XRD）. We observed that the crystallization of CuMoO_4 powder was completed at 450°C. The obtained homogeneous powder was composed of grains with sizes in the range from 150 to 500 nm and exhibited a specific surface area of approximately 5 m^2/g. The average grain size increased with increasing annealing temperature. The as-prepared CuMoO_4 crystals showed a strong green photoluminescence emission at room temperature under excitation at 290 nm, which we mainly interpreted on the basis of the Jahn-Teller effect on [MoO_4^（2-）] complex anions. We also observed that the photoluminescence intensity increased with increasing crystallite size.

Thermal decomposition of ammonium molybdate mixture

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THERMAL DECOMPOSITION OF THREE COMMERCIAL POLYPHASE AMMONIUM MOLYBDATE

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Gas-sensing Properties of Bismuth Iron Molybdate Thin Films

The thin film gas sensors of bismuth iron molybdate were prepared by ion beam sputtering technique. The prototype gas sensors studied have high sensitivity and selectivity to reducing gases, such as ethanol vapor, show a long term stability of response under most operating conditions and insensitivity to atmospheric humidity, and respond quickly comparing to traditional sintered gas sensors. The crystallographic structure and phase composition of these thin films were investigated with XRD, XPS and SEM techniques.

Synthesis,Structure and Characterization of Three Metal Molybdate Hydrates:Fe(H_2O)_2(MoO_4)_2·H_3O,NaCo_2(MoO_4)_2(H_3O_2) and Mn_2(MoO_4)_3·2H_3O

Three metal molybdate hydrates,Fe（H2O） 2（MoO4）2·H3O（FeMo）,NaCo 2（MoO4） 2（H3O2）（CoMo） and Mn 2（MoO4）3·2H3O（MnMo）,were synthesized by the mixed-solvent-thermal methods and characterized by singlecrystal X-ray diffraction.X-Ray photoelectron spectroscopy and bond-valence sums were applied to confirming the valance of Fe,Co,Mn and Mo.Thermo-gravimetric analysis and X-ray powder diffraction measurements indicate that the samples were converted to different structural compounds upon heating in air at 600 ℃ for 1 h.The magnetic properties of these compounds were studied.The dominant magnetic interactions are antiferromagnetic in nature.However,different synthesis conditions led to the diversity of magnetic properties of compound CoMo.

Effect of Molybdate Ions on the Corrosion Behaviour of Ti Alloys

Titanium alloys are extensively used in power, chemical and petroleum industries as constructional materials for vessels and heat transfer tubes. Moreover they are candidate materials for nuclear waste disposal. These alloys have superior resistance to localized forms of corrosion compared to stainless steels and Ni-base alloys. However, this resistance is not as remarkable in crevice corrosion conditions in some aggressive media. Electrochemical corrosion tests were conducted on two ASTM Ti grades namely, Ti-2 and Ti-12 in extremely low pH acidic environment. Results indicated that Ti-2 has less resistance to both general and crevice corrosion attack than Ti-12. Both alloys possess better resistance to general corrosion than to crevice corrosion. Also, results showed that the molybdate addition improves remarkably the resistance of Ti-2 to both types of attack. The increase of molybdate ions concentration from 0.03 mol/L to 0.15 mol/L made Ti-2 to be as resistant as, or somewhat higher than, Ti-12. The elecrochemical findings were further supplemented by optical examination of the corroded surface.