Catalytic dehydrogenation of cyclohexene over MoO<Subscript>3</Subscript>/γ-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalysts

A series of MoO₃/γ-Al₂O₃ catalysts with different Mo surface densities (Mo atoms/nm²) has been prepared by incipient wetness impregnation method. Structural characteristics of the prepared catalysts were investigated by atomic absorption spectroscopy, X-ray diffraction, Fourier Transform Infrared spectroscopy, N₂ adsorption at −196 °C, and temperature-programmed reduction (TPR). The catalytic activities of the prepared catalysts were tested by cyclohexene conversion between 200 and 400 °C. XRD results indicated that molybdenum oxide species were dispersed as a monolayer on the support up to 4.04 Mo atoms/nm², and the formation of crystalline MoO₃ was observed above this loading. FTIR and TPR results showed that molybdenum oxide species were present predominantly in tetrahedral form at lower loading, and polymeric octahedral forms were dominant at higher loading. Cyclohexene conversion reaction proceeded mainly through the simple dehydrogenation pathway in the studied temperature range 200–400 °C and was found to be highly dependent on MoO₃ dispersion.     

Possibility of Mo<Subscript>2</Subscript>O<Subscript>6</Subscript> formation at high temperatures in the range of pressures from 1 to 1 × 10<Superscript>−5</Superscript> bar

Gibbs free energy minimization was used to consider the formation of complex molybdenum oxide (Mo₂O₆) at 2400 K in the range of pressures from 1 to 1 to 1 × 10⁻⁵ bar for the basic component ratio Mo: O₂ = 1: 1. Several ways are shown to lead to Mo₂O₆ formation: when P = 1 bar, a synthesis reaction involving simple molybdenum oxides (MoO, MoO₂, MoO₃) is the main way; when P = 1 × 10⁻³ bar or lower, reactions of (MoO₃) _n (n = 3−5) complex oxides with metallic molybdenum and molybdenum monoxide (MoO) are.     

Study of MO2N catalyst activity and stability in CO oxidation

Unsupported molybdenum nitride powder with S_g of 115 m²g⁻¹ (passivated) has been prepared by the temperature-programmed reaction of MoO₃ in H₂/N₂ mixture. It exhibited high catalytic activity in CO oxidation. DTA experiments in the air flow and O₂ temperature-programmed pulse reaction (TPPR) showed that the optimal oxidation temperature for the Mo₂N catalyst was under 450°C because of its instability at high temperature in the presence of O₂.     

Fixation of cesium on crystalline titania with high leach-resistivity

A study of fixation of caesium on crystalline titania by co-precipitation was carried out. A maximum loading of ∼46wt% of caesium was found to be incorporated in the titania matrix. High leach-resistivity of Cs cations was observed to be in the order of 10⁻⁶–10⁻⁸ g^.m^−2.d⁻¹ by Soxhlet flow refluxing at 97 °C of the composite material calcined at 800, 1000 °C for 48 hours. The analysis of X-ray powder diffractions of the composite materials revealed that cesium was fixed in the crystal lattice of host titania with the formation of new mineral phases of CsTi₄O₉ and Cs₂Ti₅O₁₁. The results, taken together, implicate that a better fixation of caesium on titania can be achieved by calcination at 1000 °C for 48 hours.     

Electrochemical characterization of praseodymium centers in Pr<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Zr<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>O<Subscript>2</Subscript> zirconias using electrocatalysis and photoelectrocatalysis

The voltammetry of nanoparticles and scanning electrochemical microscopy are applied to characterize praseodymium centers in tetragonal and monoclinic zirconias, doped with praseodymium ions (Pr _x Zr_1−x O₂), prepared via sol–gel routes. Doped zirconia nanoparticles were synthesized by a sol–gel liquid-phase route and characterized by different techniques, including X-ray diffraction powder pattern, ultraviolet–visible diffuse reflectance spectroscopy, infrared spectroscopy, and transmission electron microscopy (TEM). Gels annealed at around 400 °C yielded tetragonal Pr _x Zr_1−x O₂ phases. The monoclinic forms of Pr-doped ZrO₂ were obtained by annealing at temperatures higher than 1,100 °C. TEM micrographs proved that the size of the nanoparticles produced was dependent on their crystalline form, around 15 and 60 nm for tetragonal and monoclinic, respectively. The electrochemical study confirmed that a relatively high content of praseodymium cation was in the chemical state (IV), i.e., as Pr⁴⁺, in both zirconia host lattices. The catalytic and photocatalytic effects of Pr⁴⁺ centers located in the monoclinic zirconia lattice on nitrite reduction and oxygen evolution reaction were studied.     

Alkylation of catechol with methanol to guaiacol over sulphate-modified zirconia solid acid catalysts

A series of sulphate-promoted ZrO₂ solid acid catalysts with different contents of SO₄ ²⁻ were calcined at 450°C in air for 4 h and tested for the liquid-phase alkylation of catechol to guaiacol in a fixed-bed down-flow reactor. The 5 wt.% SO₄ ²⁻ on ZrO₂ showed the best conversion (82%) and selectivity for guaiacol (84%) at 200°C and 1 bar pressure. A smooth correlation was observed between the catalytical activity and surface acidity of sulphated zirconia. Based on our results, a surface mechanism is proposed.     

Synthesis,characterization, and dielectric properties of β-Gd<Subscript>2</Subscript>(MoO<Subscript>4</Subscript>)<Subscript>3</Subscript> thin films prepared by chemical solution deposition

A chemical solution was employed for deposition of gadolinium molybdate [β-Gd₂(MoO₄)₃] thin films. Gadolinium acetylacetonate hydrate {[CH₃COCH = C(O–)CH₃]₃Gd·xH₂O}, molybdenum isopropoxide {Mo[OCH(CH₃)₂]₅}, and acetylacetone were used in synthesis of this molybdate. Thermal gravimetry and differential scanning calorimetry suggested that crystallization of β-Gd₂(MoO₄)₃ occurs at around 480 °C. Phase-pure, orthorhombic β-Gd₂(MoO₄)₃ films were deposited on Pt/Ti/SiO₂/Si(100) substrates. β-Gd₂(MoO₄)₃ films crystallized at 750 °C showed a strong (00l) preferred orientation. The film dielectric constant measured was 10~14 and the dielectric loss was less than 3%. There was no marked signature in the permittivity at the bulk Curie temperature, approximately 159 °C.     

The Detailed Mechanism of Oxidation of Ni-P Alloys

DTA in conjuction with X-ray diffraction analysis with a high-temperature camera and infrared spectroscopy was employed to determine the mechanism of oxidation of Ni-P alloys. Amorphous Ni-P powders were obtained from a nickel(II) sulphate bath as a nickel source and sodium dihydrophosphate(I) as a reducing agent. The crystallization product is composed of two phases: (f.c.c.) Ni and (b.c.t.) Ni₃P. The amorphous to crystalline transformation takes place in the temperature range 280–330°C. Ni₃P samples were heated from room temperature to 1050°C in air atmosphere at 5°C min⁻¹. It was found that the first stage of oxidation of Ni₃P goes through the intermediate phase of Ni₁₂P₅ formation to Ni₂P. Some exothermic reactions were observed. Heating runs were interrupted after each reaction for crystal structure determination by IR spectrometry. Infrared spectra are reported and it is shown that the structure units present in the amorphous products at about 700°C were the oxoanions PO₃ ⁻ and P₂O₇ ⁻. The final products of the oxidation process are NiO and Ni₃(PO₄)₂. This revised version was published online in July 2006 with corrections to the Cover Date.     

Kinetics of molybdenum loss from iron molybdate catalysts under nitrogen atmosphere

The loss rate of molybdenum in Fe−Mo/SiO₂ catalyst has been measured. When the catalyst is composed of a Fe₂(MoO₄)₃ crystalline phase and monolayer dispersed MoO₃, the loss rate of MoO₃ varies with the content of MoO₃ in the catalyst. If a MoO₃ crystalline phase arises in the catalyst, the loss rate will be accelerated.     

On the nature of oxygen particles in the low-temperature desorption from vanadium oxides

The nature of oxygen particles produced in low-temperature desorption from V₂O₅ and V₂O₅ · MoO₃ was studied. It was found that there was no low-temperature desorption from samples in the presence of a quartz trap cooled to −195°C, which was evidence of the absence of possible desorption of O₃ and the presence of ¹Δ_g O₂. Under these conditions, the latter was frozen completely, and ozone was not.     

Study of temperature effect on uni-univalent and uni-bivalent ion exchange reaction

Ion exchange equilibrium constant (K) for Cl⁻/Br⁻ and Cl⁻/C₂O₄²⁻ system was studied at different temperatures from 30 to 45°C. For both uni-univalent and uni-bivalent exchange systems, the value of K increases with rise in temperature i.e., from 1.16 at 30°C to 2.95 at 45°C for Cl⁻/Br⁻ system and 19.5 at 30°C to 30.0 at 45°C for Cl⁻/C₂O₄²⁻ system indicating the endothermic ion exchange reaction. The difference in K values at the same temperature for the two was related to the ionic charge of exchangeable ions in the solution. The article is published in the original.     

Adsorption of SO2 on alumina

The adsorption of SO₂ on alumina used in the aluminium industry, the so-called smelter-grade alumina, was studied in the temperature range 15–120°C. It was found that at temperatures lower than 40°C, sulphur dioxide was bonded to alumina reversibly by physical forces, and the adsorption could be described satisfactorily by the Langmuir adsorption isotherm. The heat of adsorption was estimated to be −33 kJ mol⁻¹. At temperatures ranging from 80°C to 120°C, which prevail in dry scrubbers in the aluminium industry, the heat of adsorption was determined to be −56 kJ mol⁻¹. When SO₂ was adsorbed at temperatures higher than 80°C, about 30 % of the SO₂ could not be desorbed even if the samples were heated up to 250°C. In the presence of SO₂ and oxygen, the formation of sulphate was observed at temperatures above 90°C.     

Magnesium ion-conducting gel polymer electrolytes dispersed with fumed silica for rechargeable magnesium battery application

Effect of fumed silica dispersion on poly(vinylidene fluoride-co-hexafluoropropylene)-based magnesium ion-conducting gel polymer electrolyte has been studied using various physical and electrochemical techniques. The composite gel electrolytes are free-standing and flexible films with enough mechanical strength. The optimized composition with 3 wt.% filler offers a maximum ionic conductivity of ∼1.1 × 10⁻² S cm⁻¹ at ∼25 °C with good thermal and electrochemical stabilities. The Mg²⁺ ion conduction in the gel nanocomposite film is confirmed from the cyclic voltammetry, impedance spectroscopy, and transport number measurements. The space-charge layers formed between filler particles and gel electrolyte are responsible for the enhancement in ionic conductivity. The applicability of the gel nanocomposite to a rechargeable battery is examined by fabricating a prototype cell consisting of Mg [or Mg-multiwalled carbon nanotube (MWCNT) composite] and MoO₃ as negative and positive electrodes, respectively. The discharge capacity and the rechargeability of the cell have been improved when Mg metal is substituted by Mg-MWCNT composite. The discharge capacity of the optimized cell has found to be ∼175 mAh g⁻¹ of MoO₃ for an initial ten charge–discharge cycles.     

Comparative study on uni-univalent and uni-bivalent ion-exchange reaction on Doulite A-116

Determination of ion-exchange equilibrium constant (K) for Cl⁻/I⁻ and Cl⁻/C₂O₄²⁻ system was studied at different temperatures from 25 to 45°C and by varying concentration of iodide and oxalate ion solution. For both uni-univalent and uni-bivalent exchange systems, using 0.5 g of ion-exchange resin DUOLITE A-116 (in chloride form), the value of K increases with rise in temperature i.e., from 13.0 at 25°C to 19.05 at 45°C for Cl⁻/I⁻ system and 33.0 at 25°C to 63.0 at 45°C for Cl⁻/C₂O₄²⁻ system indicating the endothermic ion-exchange reaction. The difference in K values at the same temperature for the two was related to the ionic charge of exchangeable ions in the solution.     

Thermal study on electrospun polyvinylpyrrolidone/ammonium metatungstate nanofibers: optimising the annealing conditions for obtaining WO<Subscript>3</Subscript> nanofibers

This article demonstrates how important it is to find the optimal heating conditions when electrospun organic/inorganic composite fibers are annealed to get ceramic nanofibers in appropriate quality (crystal structure, composition, and morphology) and to avoid their disintegration. Polyvinylpyrrolidone [PVP, (C₆H₉NO) _n ] and ammonium metatungstate [AMT, (NH₄)₆[H₂W₁₂O₄₀]·nH₂O] nanofibers were prepared by electrospinning aqueous solutions of PVP and AMT. The as-spun fibers and their annealing were characterized by TG/DTA-MS, XRD, SEM, Raman, and FTIR measurements. The 400–600 nm thick and tens of micrometer long PVP/AMT fibers decomposed thermally in air in four steps, and pure monoclinic WO₃ nanofibers formed between 500 and 600 °C. When a too high heating rate and heating temperature (10 °C min⁻¹, 600 °C) were used, the WO₃ nanofibers completely disintegrated. At lower heating rate but too high temperature (1 °C min⁻¹, 600 °C), the fibers broke into rods. If the heating rate was adequate, but the annealing temperature was too low (1 °C min⁻¹, 500 °C), the nanofiber morphology was excellent, but the sample was less crystalline. When the optimal heating rate and temperature (1 °C min⁻¹, 550 °C) were applied, WO₃ nanofibers with excellent morphology (250 nm thick and tens of micrometer long nanofibers, which consisted of 20–80 nm particles) and crystallinity (monoclinic WO₃) were obtained. The FTIR and Raman measurements confirmed that with these heating parameters the organic matter was effectively removed from the nanofibers and monoclinic WO₃ was present in a highly crystalline and ordered form.     

Amperometric determination of xanthine in tea,coffee, and fish meat with graphite rod bound xanthine oxidase

A method is described for construction of an amperometric xanthine biosensor based on graphite rod modified through adsorption of xanthine oxidase. Enzymatically produced H₂O₂ from xanthine was split into 2H⁺ + O₂ + 2^e− at 0.6 V and the current was measured, which was directly proportional to xanthine concentration ranging from 1 ° 10⁻⁷ to 6 ° 10⁻⁷ M with a detection limit of 1 ° 10⁻⁷ M. The biosensor exhibited optimum response within 35 sec at pH 7.0 and 35°C. It was employed for determination of xanthine in tea leaves (0.9 ° 10⁻⁵−2.5 ° 10⁻⁵ mmol/g), coffee powder (3.2 μmol/g) and fish meat (90 mmol/g). The content of xanthine in fish meat increased 6.5 times with its storage at room temperature during 15 days. The enzyme electrode could be reused 200 times during the span of 30 days, when stored in reaction buffer at 4°C.     

Thermoluminescence of photoirradiated petroleum luminophores of pyrolytic origin

Photothermoluminescence (PTL) of petroleum luminophores of pyrolytic origin was studied over a wide temperature range (−196 to 250°C). Problems related to the mechanism and stages of photochemical processes in petroleum luminophores are discussed. It was revealed that low-temperature PTL maximums at −165, −108, and −75°C are due to recombination of trapped electrons with radical cations of polycyclic aromatic hydrocarbons (PAHs) during the freezing out of the motions of H, O₂, and R^·. High-temperature (relative to the luminophore freezing points) PTL maximums at 52, 105–120, and 130–140°C are due to processes associated with the oxidation of R^·, PAHs, and olefins by ³O₂ and ¹O₂.     

The study of conditions for the preparation and application of99Mo−99mTc generators starting from irradiated molybdenum metal

⁹⁹Mo−^99mTc generators were prepared starting from irradiated molybdenum metal instead of MoO₃ in order to use reactor irradiation space more economically. The adsorption of molybdenum as sodium molybdate on different kinds of alumina was investigated. The effect of the pH of the column and the aqueous phase concentration of molybdenum were studied and related to the elution yield of^99mTc. A study of the radiation damage effect indicated that generators having a high elution efficiency of 90% could be prepared in the 100–600 mCi range. The losses of⁹⁹Mo were minimized to 10⁻⁵-10⁻⁴% and those of alumina to 2–5 μg/ml eluate.     

Electrochromic properties of MoO<Subscript>3</Subscript> thin films derived by a sol–gel process

Molybdenum trioxide (MoO₃) films were deposited on ITO/Glass substrates by the sol–gel method using a spin-coating technique and heat treated at various temperatures under different ambient atmosphere. Effects of the process parameters on the electrochromic properties of MoO₃ films were studied using cyclic voltammetry (CV) in a propylene carbonate (PC) non-aqueous solution containing 1 M lithium perchlorate (LiClO₄). Electrochromic MoO₃ film on lithium intercalation was investigated by in-situ transmittance measurement during the CV process. The MoO₃ films showed reversible recharge ability on Li⁺/e⁻ intercalation/deintercalation. Experimental results revealed that the heat-treatment temperature, the ambient atmosphere, and the thickness will have the string influence on the electrochromic properties of MoO₃ thin films. X-ray diffraction (XRD) results show that the amorphous MoO₃ films can be obtained with the heat-treatment temperature below 300 °C in O₂ ambient atmosphere. The optimum electrochromic MoO₃ film, with a thickness of 130 nm, exhibits a maximum transmittance variation (ΔT%) of 30.9%, an optical density change (ΔOD) of 0.213, an intercalation charge (Q) of 8.47 mC/cm², an insertion coefficient x in Li _x MoO₃ was 0.21 and a coloration efficiency (η) of 25.1 cm²/C between the colored and bleached states at a wavelength (λ) of 550 nm.     

Dissociation Quotients for Citric Acid in Aqueous Sodium Chloride Media to 150°C

The three molal dissociation quotients for citric acid were measured potentiometrically with a hydrogen-electrode concentration cell from 5 to 150°C in NaCl solutions at ionic strengths of 0.1, 0.3, 0.6, and 1 molal. The molal dissociation quotients and available literature data at infinite dilution were fitted by empirical equations in the all-anionic form involving an extended Debye-Hückel term and up to five adjustable parameters involving functions of temperature and ionic strength. This treatment yielded the following thermodynamic quantitites for the first dissociation equilibrium at 25°C: logK _1a=−3.127±0.002, ΔH _1a ^o =4.1±0.2 kJ-mol⁻¹, ΔS _1a ^o =−46.3±0.7 J-K⁻¹-mol⁻¹, and ΔCp _1a ^o =−162±7 J-K⁻¹-mol⁻¹; for the second acid dissociation equilibrium at 25°C: logK _2a =−4.759±0.001, ΔH _2a ^o =2.2±0.1, ΔS _2a ^o =−83.8±0.4, and ΔCp _2a ^o =−192±15, and for the third dissociation equilibrium at 25°C: logK _3a=−6.397±0.002, ΔH _3a ^o =−3.6±0.2, ΔS _3a ^o =−134.5±0.7, and ΔCp _3a ^o =−231±7.