MoO3 P2O5 Research Articles

Interpretation of experimental findings on the structure of glass in the CaO–MoO3–P2O5 system using a thermodynamic model including oxidation–reduction equilibria

This work extends the thermodynamic model of associated solutions used in the past to describe the structure and properties of glasses to the area of complex multicomponent glasses with polyvalent elements, where it has not been applied until now either due to the absence of Gibbs energies of formation of the necessary compounds or due to oxidation–reduction equilibrium in the presence of a gas phase containing oxygen. While the fitting of unknown Gibbs energies based on experimental data has already been applied to some extent in our previous work, the implementation of redox is, to the best of our knowledge, new. Four concentration series were taken from the published data from the glass-forming ternary system CaO–MoO3−P2O5: A) xMoO3−(0.5–0.75x)CaO−(0.5–0.25x)P2O5; B) xMoO3−(0.5–0.875x)CaO−(0.5–0.125x)P2O5; C) xMoO3−(0.5−x)CaO−0.5P2O5; M) xMoO3−(1−x)P2O, for which the distributions of Qn units were also published (Q denotes the PO4 tetrahedral unit with n bridging oxygens) by the 31P MAS NMR method and the Mo[V]/ΣMo fraction by the ESR method [Černošek et al. (J Solid State Chem 303:122522, 2021); Holubová et al., (J Non-Cryst Solids 607:122222, 2023)]. The following compounds were considered in the TD model: P2O5, CaO, Mo[VI]O3, Ca(PO3)2, Ca2P2O7, (Mo[VI]O2)(PO3)2, (Mo[VI]O2)2(P2O7), (Mo[VI]O2)3(PO4)2, (Mo[V]O)2(PO3)2(P2O7), (Mo[V]O)PO4. All except the hypothetical compound (Mo[VI]O2)3(PO4)2 exist, and their structure is known. Binary phosphate compounds with molybdenum lack Gibbs energies of formation. Therefore, one of the series, namely A, was used to determine these energies by nonlinear regression with the help of a genetic algorithm, without/with redox, and then the distribution of Qn units and the fraction of Mo[V]/ΣMo was predicted for the remaining series. It was found that the distribution of Qn units can be described by the TD model with redox only. During the reduction of molybdenum, the distribution of Qn unit’s changes, and thus also the connectivity of the phosphate network, for example, according to the reactions: (MoO2)2(P2O7)—> 2(MoO)PO4 + 1/2O2, in which Q1—> Q0 and 2(MoO2)(PO3)2—> (MoO)2(PO3)2(P2O7) + 1/2O2 in which Q2—> Q1. Despite the fact that the TD model with redox gives excellent agreement in the case of the Qn distribution, the agreement with the ESR measurements of the Mo[V]/ΣMo ratio is not good. The TD model predicts significantly more pentavalent molybdenum in the glass.

A Versatile VMPO Catalyst Prepared In Situ for Oxidative Ammonolysis of Isomeric Picolines and Xylenes

The V2O5–MoO3–P2O5 (VMPO) catalyst has been prepared in situ by thermal decomposition of vanado-molybdophosphoric acid (PMoV) on TiO2 support at 475°C. The TiO2 supported VMPO catalysts are characterized by FT–IR, XRD, BET surface area, NH3–TPD, and H2–TPR. Morphology of the catalyst has been studied by TEM. The accumulated data indicate decomposition of PMoV and presence of phosphate and pyrophosphate phases of molybdenum and vanadium after calcination. TPD and TPR studies exhibit the moderate acidity and presence of V4+ in the material, respectively. The VMPO catalyst has been used for ammoxidation of six different compounds including three isomeric picolines and three isomeric xylenes to the corresponding nitriles with the yield of 90–96%.

Lithium storage behavior of MoO3–P2O5 glass as cathode material for Li-ion batteries

MoO3-P2O5 glasses were prepared by a simple melt quenching method. XRD and DSC investigations confirmed the amorphous state of 60Mo-40P, 70Mo-30P and 75Mo-25P glass. Interestingly, HRTEM images revealed the inherent crystallization behavior in Mo enriched glass. The existing nanocrystals performed a synergetic effect with the glass matrix to relax the stress caused by Li ions insertion/extraction. As a result, 75Mo-25P glass with distinct nanocrystals showed excellent long cycling stability. The structural transition of MoO3-P2O5 glass and the valence change of Mo ions during cycling were discussed. Furthermore, CV and EIS measurements were performed to elucidate the difference of redox reaction, electrons transport and ions diffusion in 75Mo-25P glass and crystalline MoO3. This study provides an avenue to exploit new cathode materials with long cycling life for Li-ion batteries.

An investigation on shielding properties of BaO, MoO3 and P2O5 based glasses using MCNPX code

Abstract In the present work, some radiation shielding quantities (mass attenuation coefficients, effective atomic number, effective electron density, half value layer and mean free path) for various BaO–MoO3–P2O5 ternary glass systems have been determined within the 0.015–15 MeV energy range, using WinXCom program. Additionally, the mass attenuation coefficients of all the investigated glasses have been calculated using MCNPX simulation code (version 2.6.0) and compared to those of WinXCom results. Among the studied glasses, BaMoP8 glass sample with MoO3 content of 70% mol is found to have superior gamma-ray shielding characteristics. Moreover, the glasses studied in this paper possess better radiation shielding properties by providing shorter half value layer (HVL) than RS-253 G18 commercial glass and some concrete samples namely ordinary, hematite-serpentine and ilmanite-limonite.

Thermal properties and crystallization of BaO–MoO3–P2O5 glasses

The thermal behavior and crystallization of barium molybdate-phosphate glasses were studied in two compositional series, namely A: (100 − x)Ba(PO3)2–xMoO3 (with x = 0–70 mol%) and B: 50BaO–yMoO3–(50 − y)P2O5 (with y = 0–15 mol% MoO3). Thermal properties were studied with differential thermal analysis and dilatometry. Glass transition temperature increases in series A in the range of 0–40 mol% MoO3 and then decreases with a further increase in MoO3 content, whereas the thermal expansion coefficient in series A reveals a minimum at 50 mol% MoO3. These trends are not observed in series B, where the glass transition temperature increases in the range of 0–15 mol% MoO3 and the thermal expansion coefficient almost does not change. Crystallization of these glasses was studied by X-ray diffraction analysis, Raman and 31P MAS NMR spectroscopy. Large thermal stability of glass with a composition 35BaO–30MoO3–35P2O5 toward crystallization was demonstrated. Crystallization of glasses resulted in the formation of the compound Ba(MoO2)2(PO4)2 in this ternary system. Raman spectroscopy also provided information on the formation of glass-crystalline samples in some studied compositions.

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English

English

Thermodynamic model and Raman spectra of CaO–P2O5 glasses

Raman spectra of xZnO (100−x)P2O5 (x = 35, 40, 45, 50, 55) glasses were described by the thermodynamic model of Shakhmatkin and Vedishcheva using the method of Malfait. The glasses were considered as the ideal solution of unreacted oxides and four compounds (ZnP2O6, Zn2P2O7, Zn3P2O8, and ZnP2O11). Due to missing thermodynamic data, thermodynamic model was based on the estimates of reaction Gibbs energies of formation of considered compounds obtained by fitting the 31P MAS NMR Q-distribution in ZnO–MoO3–P2O5 glasses. Simultaneously, the set of Raman spectra was analyzed by multivariate curve resolution method. The very good coincidence between the results of spectral decomposition based on the thermodynamic model on one side and on the results of MCR method on the other can be considered as plausible validation of the thermodynamic data used, i.e., as a general guideline for the situations where the thermodynamic data needed for the construction of Shakhmatkin and Vedishcheva thermodynamic model are missing but the detailed structural information is available.

Thermal properties and crystallization of PbO–MoO3–P2O5 glasses

Thermal properties and crystallization of glasses from PbO–MoO3–P2O5 ternary system were studied in three compositional series (100 − x)[0.5PbO–0.5P2O5]–xMoO3 (A), 50PbO–yMoO3–(50 − y)P2O5 (B), and (50 − z)PbO–zMoO3–50P2O5 (C). Glass transition temperature, crystallization temperature, coefficient of thermal expansion, and dilatation softening temperature of the studied glasses were determined by differential thermal analysis and dilatometry. Crystallization products of annealed glass samples were investigated by X-ray diffraction and Raman spectroscopy. X-ray diffraction analysis of crystallized glasses revealed the formation of PbP2O6, Pb3P4O13, and PbMoO4 in the samples of the B series. In the series A and C in the samples with a high MoO3 content, crystalline compounds of Pb(MoO2)2(PO4)2 and (MoO2)(PO3)2, respectively, were identified. Raman spectra of crystalline samples confirmed the results of X-ray diffraction measurements and provided also information on thermal stability of glasses and formation of glass-crystalline phases in the studied glass series.

Crystallization and physical properties of alkali phosphomolybdate glasses containing niobium oxide

AbstractGlasses with transition metal ions have interest because of their potential use in electrochemical, electronic and electro‐optical devices. Molybdenum oxide is not a glass‐forming, but it is able to enter the glass structure in the form of MoO4 tetrahedral or MoO6 octahedral with some glass‐forming, like P2O5. The binary MoO3–P2O5 glasses were stable over a wide range of compositions. The ternary glass P2O5–MoO3–Li2O presents high potentiality as fast ion‐conductors. Ferroelectric crystalline particles (LiNbO3) can be obtained by heat‐treatments of the glass P2O5‐Li2O‐Nb2O5. The heat‐treatment does not promote glass‐ceramics with a single crystalline phase. The quaternary system P2O5‐MoO3‐Nb2O5‐X2O, (X=Li, Na), prepared by melt quenching, allowed the control of the crystalline phases obtained by heat‐treatments. In this work, the transparent as‐prepared glasses were heat‐treated at 550 ºC and 650 ºC for 4 hours. The structure of the samples was analyzed by differential thermal analyses (DTA), X‐ray powder diffraction (XRD), scanning electron microscopy (SEM) and Raman spectroscopy. The change of the MoO3/P2O5 ratio is the main chemical parameter that governs the nucleation and growth of different crystallites. The decrease of this ratio induces the formation of non‐linear optical NbOPO4 crystallites in the glass. The increase of the ratio leads to the formation of other phases, such as LiPO3 (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Structural study of PbO–MoO3–P2O5 glasses by Raman and NMR spectroscopy

Glasses in the ternary system PbO–MoO3–P2O5 were prepared in three compositional series (100−x)[0.5PbO–0.5P2O5]–xMoO3 (A), 50PbO–yMoO3–(50−y)P2O5 (B) and (50−z)PbO–xMoO3–50P2O5 (C) and their structure was studied by Raman and 31P NMR spectroscopies. In the compositional series (100−x)[0.5PbO–0.5P2O5]–xMoO3 homogeneous glasses were prepared in the concentration region of 0–70mol% MoO3. Their glass transition temperature increases with increasing MoO3 content having a maximum at x=50mol% MoO3. 31P MAS NMR spectra reveal that in the glass series (A) the incorporation of MoO3 results in the shortening of phosphate chains and gradual transformation Q2 units into Q2 and Q0 units, prevailing in glasses with a high MoO3 content. Octahedral structural units MoO6 dominate in most glass compositions and they are present also in the structure of Pb(MoO2)2(PO4)2 compound corresponding to the glass composition 50Pb(PO3)2–50MoO3. The analysis of Raman spectra of glasses of the (B) series with a high MoO3 content showed the transformation of octahedral MoO6 units into tetrahedral MoO4 units.

Ag concentration dependent transport properties of LiF–MoO3–P2O5 glasses

Abstract LiF–MoO3–P2O5 glasses mixed with different concentrations of Ag2O (ranging from 0 to 1.0 mol%) was prepared. D.C. conductivity and dielectric properties over a range of temperature have been investigated. The analysis of the results of d.c. conductivity has indicated that T>θD/2, the small polaron hoping model seems to be fit and the conduction is adiabatic in nature. These results further indicated that there is a change over of conduction mechanism from electronic to ionic at about 0.4 mol% of Ag2O. The low temperature part of a.c. conductivity is explained based on quantum mechanical tunneling model. The quantitative analysis of these results is further extended with the aid of the data on optical absorption, ESR and IR spectral studies.

Electrical switching in the MoO3–WO3–P2O5 and MoO3–P2O5 glasses

High field electrical switching on blown films of MoO3(60%)–P2O5(40%), MoO3(50%)–WO3(10%)–P2O5(40%), and MoO3(45%)–WO3(15%)–P2O5(40%) having different thicknesses was studied and compared. Switching was observed using two terminal samples. S-type current–voltage characteristic (current-controlled negative resistance—CCNR) with memory was observed in molybdenum–phosphate glasses, but N-type characteristic (voltage-controlled negative resistance—VCNR) with threshold in tungsten–molybdenum–phosphate glasses was observed. The important observation was that with the addition of WO3 to binary MoO3–P2O5 led to a change of I–V characteristic from CCNR with memory to VCNR with threshold. The measurements of density and molar volume showed linear relation between MoO3 content and density which decreased with the increase of MoO3 content. The samples’ thickness had no significant effect on threshold voltage. The attained results also indicated that the electrode material had no effect on switching property of devices. The switching behavior of the devices did not show any dependence on the polarity of the applied voltage. In terms of the effect of heat on the switching behavior of molybdenum–phosphate glasses, it was found that threshold voltage decreases with increasing of temperature. Finally, the switching phenomenon was explained by thermal (formation of crystalline filaments) and electronic models.

Optical properties of glasses in the Li2O–MoO3–P2O5 system

Glasses xLi2O–(50-x)(MoO3)2–50P2O5 with x = 10, 20, 30, and 40 mol% were prepared and their optical and electrical properties were investigated. Analysis of the IR spectra revealed that the Li+ ions act as a glass modifier that enter the glass network by breaking up other linkages and creating non-bridging oxygens in the network. The optical absorption edge of the glasses was measured for specimens in the form of thin blown films and the optical absorption spectra of those were recorded in the range 200–800 nm. From the optical absorption edges studies, the optical band gap (E opt) and the Urbach energy (E e) values have been evaluated by following the available semi-empirical theories. The linear variation of (αhν)1/2 with hν, is taken as evidence of indirect interband transitions. The E opt values were found to decrease with increasing Li2O content by causing increase in the number of non-bridging oxygens in network. The Urbach tail analysis gives the width of localized states between 0.48 and 0.74 eV.

ChemInform Abstract: PRODUCTION OF FURAN BY VAPOR‐PHASE OXIDATION OF CROTONALDEHYDE USING HETEROPOLY COMPOUNDS AS CATALYSTS

AbstractDie Synthese von Furan (II) durch direkte Dampfphasen‐ Oxidation von Crotonaldehyd (I) wird untersucht.

Production of Furan by Vapor-phase Oxidation of Crotonaldehyde Using Heteropoly Compounds as Catalysts

Abstract The synthesis of furan by direct vapor-phase oxidation of crotonaldehyde has been studied. It was found that heteropoly compounds such as 12-molybdophosphoric acid are more effective than the mixed oxide (MoO3–P2O5, P/Mo=1/12) as catalyst for furan formation, and that the cesium salt of 12-molybdophosphoric acid with a Cs/Mo atomic ratio of 1/12 is more effective than the 12-molybdophosphoric acid catalyst. The rate of furan formation increases with increase in steam concentration in the feed, but is nearly independent of oxygen and crotonaldehyde concentrations. The yield of furan increases by decreasing the crotonaldehyde concentration, attaining 60 mol% at a concentration of 0.17 vol% in the feed. The conversion of crotonaldehyde at maximum yield is 90–95%.

Acidic Property and Oxidation Activity of MoO3-V2O5-P2O5 Ternary Oxides

Abstract The relationship between the acid-base properties and the oxidation activity of a series of ternary oxide catalysts, MoO3–V2O5–P2O5, with different V/Mo composition and a constant phosphorus content, P/(Mo+V)=0.1, was investigated. The acidity was determined by means of the NH3 adsorption and by studying the catalytic activity for acid-catalyzed reactions, such as dehydration of isopropyl alcohol and isomerization of 1-butene, in the presence of an excess of air. A new acidic site is generated by the combination of two binary oxides, i.e., MoO3–P2O5 and V2O5–P2O5, and a broad maximum in the acidity occurs at V/(Mo+V)=0.4–0.9. The basic property is so small that no satisfactory data can be obtained from the adsorption of acidic molecules such as CO2, SO2, and acetic acid. The catalysts, regardless of composition, are inactive for reactions which are accelerated by basic sites, such as oxidative dehydrogenation of isopropyl alcohol to acetone, oxidative decomposition of formic acid to CO2, and oxidation of methanol to CO2. The oxidation activities for butadiene and methanol can be tied to the acidity of the catalysts.

A Study of the Catalytic Partial Oxidation of Hydrocarbons. XI. The Catalytic Activity of the MoO3–P2O5 and the MoO3–Bi2O3–P2O5 in the Selective Oxidation of Butene, Butadiene, and Furan

Abstract In the present work, the vapor-phase partial oxidation of cis-2-butene, butadiene, furan, and maleic anhydride was carried out over MoO3–P2O5 (1 : 0.2 atomic ratio) and MoO3–Bi2O3–P2O5 (1 : 1 : 0.2) with a contact time of 1.6 sec, at a concentration of 0.6–1.0%, and in air, in order to elucidate the difference between the two catalysts in their catalytic specificity for the oxidation of these reactants to maleic anhydride. Over the MoO3–P2O5 catalyst, the selectivities of butene, butadiene, and furan to maleic anhydride were 13, 50, and 78% respectively. Over the MoO3–Bi2O3–P2O5 catalyst, the formation of maleic anhydride from the reactants was very small, that of CO2 was important, and the rate of maleic anhydride destruction was fairly high. It is considered that the MoO3–Bi2O3–P2O5 catalyst has almost the same catalytic specificity as the MoO3–P2O5 in the C4H8→C4H2O3 step, but that its activity for maleic anhydride destruction is so high that maleic anhydride cannot be accumulated.