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The MoO3/Al2O3 catalytic systems were studied. The catalysts, were highly selective and moderately active in propene metathesis at a low temperature (303 K). It was shown by XPS that preliminary thermal treatment of the catalysts ...
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The MoO3/Al2O3 catalytic systems were studied. The catalysts, were highly selective and moderately active in propene metathesis at a low temperature (303 K). It was shown by XPS that preliminary thermal treatment of the catalysts affects their final reactivity towards propene. The surface of the molybdena-alumina catalyst, which was evacuated at 523 K and then activated at 873 K in argon, underwent partial reduction to Mo-V phase under the influence of propene at 303 K. This effect was not observed in the case of the molybdena-alumina catalyst, which was calcinated at 823 K and then analogously activated. It was concluded that the reducibility of the surface molybdenum was connected with the activity of the catalyst in propene metathesis. It was proposed that the difference of the reactivity towards propene of both catalysts was caused by the difference in the homogeneity of the surface molybdenum. It was stated that the activation of the catalysts in argon at 873 K increased the homogeneity of the surface molybdenum. (C) 2000 Elsevier Science B.V. All rights reserved. [References: 19]
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The paper proposes a new theoretical model based on local thermodynamic equilibrium enabling the prediction of gas generation during the reaction of aluminum-based thermites. We demonstrate that the model has the capability to pre...
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The paper proposes a new theoretical model based on local thermodynamic equilibrium enabling the prediction of gas generation during the reaction of aluminum-based thermites. We demonstrate that the model has the capability to predict the total pressure and the partial pressures of its components as a function of the reaction extent and compaction. Al/CuO, Al/Bi2O3, Al/Sb2O3, Al/MoO3, and Al/WO3 thermites are modeled and their capability to generate pressure is compared. Simulation results are also validated through dedicated experiments and show general agreement beyond the state of the art. Mechanisms underlying pressure generation are detailed. A two-stage process for the pressure increase in Al/CuO reaction, also observed experimentally, is shown to be driven by oxygen generation as produced by CuO and Cu2O vaporization through different kinetics. Comparison with experimental data stresses the issue of understanding the complex chemical processes taking place during vaporization and subsequent gas phase reactions and the need to determine their thermodynamic constants.
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As the most important component for MEMS-based pyrotechnics, the micrometer should generate enough energy to successfully ignite the next explosive. An enhanced reactive igniter was designed and fabricated through sputtering the A...
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As the most important component for MEMS-based pyrotechnics, the micrometer should generate enough energy to successfully ignite the next explosive. An enhanced reactive igniter was designed and fabricated through sputtering the Al/CuO nanolaminates onto the NiCr micro-heater to enhance the output energy of the NiCr micro-heater. The average thickness of the Al/CuO nanolaminate is 6.84 mu m, and the designed thickness is 6 mu m. The grain sizes of Al/CuO nanolaminates are not uniform, and the particle grains of the Al/CuO nanolaminates at the top are smaller than those at the bottom. When the applied currents passed through the igniter, the resistance of the igniter changed dynamically, leading to the igniter experiencing three stages. Compared to the bare NiCr micro-heater without depositing Al/CuO nanolaminates, the enhanced reactive igniter can successfully ignite Zr/KClO4 explosive, indicating that the Al/CuO nanolaminates could enhance the output capability of the NiCr micro-heater. It is of vital importance to guide the design of MEMS-based pyrotechnics.
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In order to improve thermal conductivity, energy performance, and combustion performance of the aluminum-containing thermite, nanocarbon materials were added to thermite. Aluminum/molybdenum and trioxide/nanocarbon materials (Al/M...
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In order to improve thermal conductivity, energy performance, and combustion performance of the aluminum-containing thermite, nanocarbon materials were added to thermite. Aluminum/molybdenum and trioxide/nanocarbon materials (Al/MoO3/NCM) were fabricated by electrostatic spinning technology. The Al and MoO3 particles of the nAl/MoO3/NCM thermite are much smaller than nitrocellulose (NC); thus, the two components can be better attached to NC fibers. Results on thermal conductivity demonstrated that the addition of NCM can improve the thermal conductivity of Al/MoO3, and the addition of reduced graphene oxide (RGO) has a more significant impact on thermal conductivity. Energy performance analysis results indicated that the energy performance of Al/MoO3/NCM thermite spinning is the best when the value of combustion oxygen equivalent ratio (Φ) is 0.90–1.00. The combustion performance results show that the addition of NCM can significantly increase the combustion rate of thermites, and the addition of RGO improves its combustion rate the most, followed by carbon nanotubes (CNT) and nanoflake graphite (NFG) being the lowest. By changing the shape of the Al/MoO3/NCM charge and the internal composition of the charge, the sensitivity of the agent can be adjusted, and the matching performance and use performance of the electric igniter can be improved.
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Herein, a novel MoO3/Zn-Al LDHs composite photocatalyst was successfully prepared. Morphology, chemical composition, and photoelectrochemical properties of the prepared catalyst were explored by different characterization methods,...
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Herein, a novel MoO3/Zn-Al LDHs composite photocatalyst was successfully prepared. Morphology, chemical composition, and photoelectrochemical properties of the prepared catalyst were explored by different characterization methods, including X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), X-ray photoelectron spectroscopy (XPS), Brunauer Emmett-Teller (BET), UV-Vis diffuse reflectance spectrometry (DRS) and Electron Spin Resonance (ESR). Using tetracycline as a target pollutant, the photocatalytic activity of MoO3 (10 wt%)/Zn-Al LDHs composite was tested by photodegradation of tetracycline under visible light irradiation. The experimental results indicate that the MoO3 (10 wt%)/Zn-Al LDHs composite exhibited higher photocatalytic removal efficiency than pure Zn-Al LDHs and MoO3. The removal efficiency of TC in 60 min could reach 90.5%. It was confirmed that the optimal conditions were a catalyst dosage of 1.0 g/L, an initial pH of 9, and an initial concentration of TC of 40 mg/L. In addition, a possible mechanism for the photodegradation of TC with MoO3 (10 wt%)/Zn-Al LDHs composite was proposed. The introduction of MoO3 facilitates the separation of electron-hole pairs. It could be seen that the MoO3 (10 wt%)/Zn-Al LDHs composite has great application prospects for the treatment of antibiotic wastewater.
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The equilibrium properties of bulk MgMoO4, Zr(MoO4)2, Al2(MoO4)3, SrMoO4, and Cr2(MoO4)3 have been characterized by coulometric titration at 873 K in order to understand the effect of the mixed-cation environment on the Mo~(6+)-Mo...
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The equilibrium properties of bulk MgMoO4, Zr(MoO4)2, Al2(MoO4)3, SrMoO4, and Cr2(MoO4)3 have been characterized by coulometric titration at 873 K in order to understand the effect of the mixed-cation environment on the Mo~(6+)-Mo~(4+) redox properties and how this in turn affects reactivity for methanol oxidation. The structures of the oxidized and reduced phases were also characterized by XRD. With SrMoO4, reduction resulted in the formation of SrMoO3; however, each of the other oxides underwent a reversible decomposition. MgMoO4 formed a mixture of crystalline MgO and Mg2Mo3O8; Zr(MoO4)2 reduced to MoO2 and a mixture of monoclinic and tetragonal ZrO2; and Cr2(MoO4)3 formed a new crystalline phase. For MgMoO4, Zr(MoO4)2, Al2(MoO4)3, and Cr2(MoO4)3, removal of one O/Mo occurred at a P(O2) of 10~(-6) atm, corresponding to a ΔG of oxidation of-100kJ/mol-O2; however, the equilibrium between SrMoO4 and SrMoO3 occurred at 10~(-26) atm O2, corresponding to a ΔG of oxidation equal to -375 kJ/mol-O2. These thermodynamic properties differ significantly from oxidation of MoO2 to MoO3, for which ΔG is -220 kJ/mol-O2 at 873 K. All of the mixed oxides were essentially inactive for the selective oxidation of methanol, with specific rates that were much lower than that observed for M0O3.
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Controlled reduction by hydrogen, of the equivalent five monolayer of MoO3 deposited on TiO2 as a function of the reduction temperature up to 873 K, enabled us to obtain three Mo2O5, bifunctional (metal-acid) MoO2(H_x)_(ac) and th...
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Controlled reduction by hydrogen, of the equivalent five monolayer of MoO3 deposited on TiO2 as a function of the reduction temperature up to 873 K, enabled us to obtain three Mo2O5, bifunctional (metal-acid) MoO2(H_x)_(ac) and the metallic Mo(0) phases. Characterization of these phases was made by employing surface XPS-UPS techniques in parallel with catalytic reactions. Hydroisomerization of n-hexane occurs on the bifunctional phase, while hydrogenation/ dehydrogenation and benzene formation were performed by the metallic Mo state.
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摘要 :Controlled reduction by hydrogen, of the equivalent five monolayer of MoO3 deposited on TiO2 as a function of the reduction temperature up to 873 K, enabled us to obtain three Mo2O5, bifunctional (metal-acid) MoO2(Hx)ac and the me...
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Controlled reduction by hydrogen, of the equivalent five monolayer of MoO3 deposited on TiO2 as a function of the reduction temperature up to 873 K, enabled us to obtain three Mo2O5, bifunctional (metal-acid) MoO2(Hx)ac and the metallic Mo(0) phases. Characterization of these phases was made by employing surface XPS-UPS techniques in parallel with catalytic reactions. Hydroisomerization of n-hexane occurs on the bifunctional phase, while hydrogenation/ dehydrogenation and benzene formation were performed by the metallic Mo state.
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A new heterogeneous sonocatalytic system consisting of a MoO3/Al2O3 catalyst and H2O2 combined with ultrasonication was studied to improve and accelerate the oxidation of model sulfur compounds of diesel, resulting in a significan...
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A new heterogeneous sonocatalytic system consisting of a MoO3/Al2O3 catalyst and H2O2 combined with ultrasonication was studied to improve and accelerate the oxidation of model sulfur compounds of diesel, resulting in a significant enhancement in the process efficiency. The influence of ultrasound on properties, activity and stability of the catalyst was studied in detail by means of GC-FID, PSD, SEM and BET techniques. Above 98% conversion of DBT in model diesel containing 1000 mu g/g sulfur was obtained by new ultrasound-assisted desulfurization at H2O2/sulfur molar ratio of 3, temperature of 318 K and catalyst dosage of 30 g/L after 30 min reaction, contrary to the 55% conversion obtained during the silent process. This improvement was considerably affected by operation parameters and catalyst properties. The effects of main process variables were investigated using response surface methodology in silent process compared to ultrasonication. Ultrasound provided a good dispersion of catalyst and oxidant by breakage of hydrogen bonding and deagglomeration of them in the oil phase. Deposition of impurities on the catalyst surface caused a quick deactivation in silent experiments resulting only 5% of DBT oxidation after 6 cycles of silent reaction by recycled catalyst. Above 95% of DBT was oxidized after 6 ultrasound-assisted cycles showing a great improvement in stability by cleaning the surface during ultrasonication. A considerable particle size reduction was also observed after 3 h sonication that could provide more dispersion of catalyst in model fuel. (C) 2013 Elsevier B.V. All rights reserved.
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MoO3-Al composite powders were used for preparing in situ composite coatings. Effects of the composition of MoO3-Al composite powder on the microstructure and properties of the as-prepared coatings were investigated. The results s...
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MoO3-Al composite powders were used for preparing in situ composite coatings. Effects of the composition of MoO3-Al composite powder on the microstructure and properties of the as-prepared coatings were investigated. The results show that the main phases of the as-prepared coatings were gamma-Al2O3 and Mo. An optimal composition (63 wt%) of MoO3 in MoO3-Al composite powder was demonstrated. The porosity of the as-prepared composite coatings decreased first and then increased with the increase of MoO3. This is attributed to the fact that the melting state of the powder during plasma spraying is closely involved in the content of MoO3. The coating prepared by composite powder with 63 wt% MoO3 had the most Al2O3 and the highest microhardness. The wear resistance of 63 wt% MoO3 composite coating was the best among four coatings with different content of MoO3, which is attributed to its high hardness and good toughness.
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