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1.
The structural development of the NiFe 2O 4 nanocrystals dispersed in a silica matrix was followed by IR and EPR spectroscopies of the dried gel 10NiO–10Fe 2O 3–90SiO 2 after heat treatment. The dried gel obtained at 200°C was amorphous, in which Fe 3+ and Ni 2+ ions were distributed in the pores of silica matrix. When the dried gel was heat treated at 400°C, NiFe 2O 4 clusters were partially formed, showing an enhanced interaction with the silica matrix. NiFe 2O 4 clusters were completely formed in silica matrix when the heat treatment was increased to 600°C, at which the interactions between the clusters and silica matrix reached a maximum. The formation reaction of NiFe 2O 4 clusters was accompanied by a rearrangement of the silica matrix network. Further increase of the heat treatment temperature to 800°C led to superparamagnetic single domain NiFe 2O 4 nanocrystals (ca. 4 nm) dispersed in the silica matrix with the elimination of the interactions between magnetic nanocrystals and silica matrix. 相似文献
2.
To develop porous alumina supported MF ZrO 2 membranes, ZrO 2–Al 2O 3 composite intermediate layers are considered in order to decrease stress creation during the processing and avoid cracks formation. The relation between distortion stress and sintering shrinkage was experimentally studied. And the cracks formation mechanism was qualitatively evaluated and discussed. Finally, crack-free YSZ membrane with pore size of 0.16 μm on the two ZrO 2–Al 2O 3 intermediate layers possessing a gradient composition was successfully prepared and characterized. 相似文献
3.
A new class of proton conducting glass membranes for hydrogen fuel cell applications are being developed using phosphotungstic acid. These glasses are being design to yield high proton conductivities could be potential substitutes for electrolytes in H 2/O 2 fuel cell. P 2O 5–SiO 2–PWA glasses have been non-crystalline phases confirmed by structural studies. The glass materials showed good mechanical and thermal stability, and also found a maximum proton conductivity of 9.1 × 10 −2 S/cm at 90 °C and 30% RH. The average pore size less than 5 nm was determined by Barrett–Joyner–Halenda (BJH) desorption method. The electrochemical activity was investigated by polarization curves and current–voltage profiles. A maximum power density value of 10.2 mW/cm 2 was obtained using 0.15 mg/cm 2 of Pt/C loaded on electrode and 5P 2O 5–87SiO 2–8PWA glasses at 30 °C and 30% humidity. 相似文献
4.
Al 2O 3–ZrO 2 mixed supports have been synthesised using a colloidal solution of ZrO(OH) 2 or a Zr(IV) propoxide solution in organic medium. Zirconia content in these samples was about 10% (36% of the theoretic monolayer). The hydrothermal stability (alumina→boehmite transformation at 230 °C, about 10 bar pressure, in the presence of water vapour) of these supports was then investigated by XRD. The presence of the zirconia over the alumina decrease the quantity of boehmite formed after the hydrothermal treatment. The dispersion of zirconia and the stability in hydrothermal conditions of the final support are function of the preparation method. 相似文献
5.
Aerosol flame pyrolysis deposition method was applied to deposit the oxide glass electrolyte film and LiCoO 2 cathode for thin film type Li-ion secondary battery. The thicknesses of as-deposited porous LiCoO 2 and Li 2O–B 2O 3–P 2O 5 electrolyte film were about 6 μm and 15 μm, respectively. The deposited LiCoO 2 was sintered for 2 min at 700 °C to make partially densified cathode layer, and the deposited Li 2O–P 2O 5–B 2O 3 glass film completely densified by the sintering at 700 °C for 1 h. After solid state sintering process the thicknesses were reduced to approximately 4 μm and 6 μm, respectively. The cathode and electrolyte layers were deposited by continuous deposition process and integrated into a layer by co-sintering. It was demonstrated that Aerosol flame deposition is one of the good candidates for the fabrication of thin film battery. 相似文献
6.
The kinetic parameters including the activation energy for crystallization ( E), the Avrami parameter ( n) and frequency factor ( υ) of a glass in the MgO–CaO–SiO 2–P 2O 5–F system were studied using non-isothermal differential thermal analysis (DTA) with regard to small amount of TiO 2 additions. It has been shown that the role of TiO 2 changes from a glass network former to a glass network modifier with increasing TiO 2 content in this system. The kinetic parameters of the crystallizing phases, apatite and wollastonite, indicated changes accompanied with TiO 2 additions, implying that the TiO 2 is an effective nucleating agent for promoting the crystallization of apatite and wollastonite. The most effective addition is of about 4 wt% TiO 2 in this system. The wear rate and friction coefficient decreased from 1.8 ± 0.1 to 0.9 ± 0.2 and 0.87 to 0.77, respectively, when 4 wt% TiO 2 was incorporated to the base glass. 相似文献
7.
This work presents chemical modeling of solubilities of metal sulfates in aqueous solutions of sulfuric acid at high temperatures. Calculations were compared with experimental solubility measurements of hematite (Fe 2O 3) in aqueous ternary and quaternary systems of H 2SO 4, MgSO 4 and Al 2(SO 4) 3 at high temperatures. A hybrid model of ion-association and electrolyte non-random two liquid (ENRTL) theory was employed to fit solubility data in three ternary systems H 2SO 4–MgSO 4–H 2O, H 2SO 4–Al 2(SO 4) 3–H 2O at 235–270 °C and H 2SO 4–Fe 2(SO 4) 3–H 2O at 150–270 °C. Employing the Aspen Plus™ property program, the electrolyte NRTL local composition model was used for calculating activity coefficients of the ions Al 3+, Mg 2+ Fe 3+ and SO 42−, HSO 4−, OH −, H 3O +, respectively, as well as molecular species. The solid phases were hydronium alunite (H 3O)Al 3(SO 4) 2(OH) 6, hematite Fe 2O 3 and magnesium sulfate monohydrate (MgSO 4)·H 2O which were employed as constraint precipitation solids in calculating the metal sulfate solubilities. A correlation for the equilibrium constants of the association reactions of complex species versus temperature was implemented. Based on the maximum-likelihood principle, the binary interaction energy parameters for the ionic species as well as the coefficients for equilibrium constants of the reactions were obtained simultaneously using the solubility data of the ternary systems. Following that, the solubilities of metal sulfates in the quaternary systems H 2SO 4–Fe 2(SO 4) 3–MgSO 4–H 2O, H 2SO 4–Fe 2(SO 4) 3–Al 2(SO 4) 3–H 2O at 250 °C and H 2SO 4–Al 2(SO 4) 3–MgSO 4–H 2O at 230–270 °C were predicted. The calculated results were in excellent agreement with the experimental data. 相似文献
8.
One-pot condensation of β-dicarbonyl compounds with aldehydes and ammonium acetate in the presence of HClO 4–SiO 2 at 80 °C under solvent-free conditions with good to excellent yields. The catalyst is easily prepared, stable, reusable and efficiently used under reaction conditions. 相似文献
9.
Titania–zirconia mixed oxides with various ZrO 2 content in TiO 2 (10, 50 and 90 wt.%) were prepared by the sol–gel method. High specific surface areas (77–244 m 2/g) were obtained. Acidity determined by NH 3-TPD and FTIR-pyridine adsorption showed that in mixed oxides the number of acid sites is dramatically increased; it varies from 173 μmol NH 3/g for TiO 2 to 1226–1456 μmol NH 3/g for the mixed oxides. FTIR-pyridine adsorption showed the presence of Lewis sites in the catalysts. Basic sites were identified by FTIR-CO 2 adsorption, suggesting the formation of mixed oxides with acid–basic properties. XRD spectra identified anatase in the TiO 2 rich region, amorphous material in the mixed oxide 50–50 TiO 2–ZrO 2 and tetragonal and monoclinic crystalline phases in the ZrO 2 rich region. Activity in the isopropanol decomposition showed a good correlation between the acid–basic properties and the selectivity to propene, acetone and isopropyl ether. The latter was found as a product which mainly depends of the acid sites density. 相似文献
10.
Palladium, silver and palladium–silver catalysts supported on silica were prepared by coimpregnation of support with solution of AgNO 3 and Pd(NO 3) 2. The catalysts were characterized by X-ray powder diffraction (XRD), temperature programmed reduction (TPR), time of flight ion mass spectrometry (ToF-SIMS), chemisorption of carbon monoxide and were tested in the reaction of selective oxidation of glucose to gluconic acid. XRD and TPR studies have shown that an interaction between Pd and Ag on the surface of silica after oxidation at 500 °C and reduction at 260 °C leads to the formation of solid solutions. ToF-SIMS images of the surface of 5% Ag/SiO2 catalyst after oxidation at 500 °C and reduction at 260 °C show that Ag atoms supported on silica are not distributed homogenously but tend to form regions of enhanced Ag concentration. Positive ions images of the surface of 5% Pd/SiO2 catalyst also display regions of enhanced concentration of Pd atoms, but they are more homogenously distributed on silica. ToF-SIMS peak intensity ratio 108Pd+/107Ag+ for bimetallic 5% Pd–5% Ag/SiO2 catalysts has a lower value than that obtained for physical mixture 5% Pd/SiO2–5% Ag/SiO2 which indicates that the surface of bimetallic catalyst is enriched with silver atoms. 相似文献
11.
The mechanism of the SO 2 + HO 2 reaction was studied theoretically for the first time. Three product channels were revealed, namely, O 2 + HOSO, O 2 + HSO 2, and OH + SO 3. The O 2 + HOSO channel dominates the reaction under combustion conditions. A five-member-ring complex [SO 2–HO 2] exists at the entrance of the reaction. The structure and binding energy ( De and D0) of the SO 2–HO 2 complex have been calculated. In view of D0 = 21.2 ± 2.0 kJ mol −1, the SO 2–HO 2 complex should be stable at low temperature. The infrared spectra and frequency shifts were calculated for both SO 2–HO 2 and SO 2–DO 2, and compared with the available experimental data. 相似文献
12.
采用液相沉积法(LPD)制备了纳米氧化锆沉积硅胶色谱固定相(ZrO 2/SiO 2), 并将其应用于亲水作用色谱分离中. 考察并比较了ZrO 2/SiO 2、 硅胶(SiO 2)和氧化锆(ZrO 2) 3种色谱固定相在不同有机调节剂比例、 不同pH值及不同盐浓度的流动相条件下的色谱行为. 结果表明, 制备的ZrO 2/SiO 2色谱柱不仅具有SiO 2色谱柱高柱效的优点, 表面沉积的纳米氧化锆还能有效屏蔽硅羟基, 有利于碱性物质的保留和分离, 表现出良好的亲水作用色谱性能. 将ZrO 2/SiO 2色谱柱用于4种脱氧核苷和5种碱性化合物的分离, 均得到了较好的效果, 展现出其作为色谱固定相良好的应用前景. 相似文献
13.
To study the effect of W concentration and activation temperature of the catalysts a series of WO x/ZrO 2 samples with varying concentration of W (10–25 wt.%) were prepared and activated at 650/750 °C. XRD of sample shows 15 wt.% W stabilizes the tetragonal phase of zirconia up to 750 °C. Above and less than 15 wt.% shows peaks corresponding to monoclinic WO 3 and monoclinic ZrO 2, respectively. Further, the tungsten modification stabilizes the specific surface area of ZrO 2. There is an increase in the surface area observed up to 15 wt.% W, which declines on further increase in the concentration. The NH 3 TPD confirms the presence of acid sites with varying strength from the broad desorption profile. The 15 wt.% W and activated at 750 °C shows maximum acidity. The results of the nitration reaction of chlorobezene imply the 15 wt.% W and activation at 750 °C shows maximum activity. Not only yield, a better para-selectivity is also achieved with WO x/ZrO 2 samples. Effect of activation temperature, W concentration and reaction parameters such as reaction temperature, reaction time, the presence of solvent and solvent free medium on activity and selectivity are studied in details. 相似文献
14.
Electrocatalytic water oxidation to evolve O 2 was studied on a Nafion–RuO 2–Ru(bpy) 32+ composite electrode. The O 2 evolution current efficiency was largely improved for the multi-component electrode over the Nafion–RuO 2 and Nafion–Ru(bpy) 32+ individuals. The redox mediation through the Ru(bpy) 32+ was found to dominate over the RuO 2 catalytic effect in the water oxidation mechanism. The specific surface area of the RuO 2, which was prepared at different temperatures (300–700°C), used in fabricating the composite electrode also played an important role in the overall water oxidation mechanism. Both the reaction and electrode parameters were optimized to get effective electrocatalytic current values in this study. 相似文献
15.
The reaction between SiCl 4 and O 2 at 1 atm between 25 and 1200°C has been followed by mass spectrometry. Below 600°C no reaction with O 2 is noted. Above 600°C the reaction proceeds in two steps. Between 800 and 1000°C the 28Si/ 32O 2 peak height ratio is constant with no evolution of Cl 2. It is suggested that silicon oxychlorides are being formed in this temperature regime. Above 1000°C the reaction between SiCl 4 and O 2 intensifies with concomitant production of Cl 2. It is suggested that above 1000°C the reaction SiCl 4 + O 2 → SiO 2 + Cl 2 becomes important. At low temperatures (<800°C) adsorbed H2O and OH groups from the surface of the fused silica tube react with SiCl4 to form HCl. The importance of this reaction decreases with increasing temperature. The increased production of HCl above 1000°C is ascribed to H2O and H2 diffusing from the tube. 相似文献
16.
Fine particle superacidic sulfated zirconia (SO 42−/ZrO 2, S-ZrO 2) was synthesized by ameliorated method, and composite membranes with different S-ZrO 2 contents were prepared by a recasting procedure from a suspension of S-ZrO 2 powder and Nafion solution. The physico-chemical properties of the membranes were studied by ion exchange capacity (IEC) and liquid water uptake measurements, scanning electron microscopy (SEM) and X-ray diffraction (XRD) analysis, thermogravimetry–mass spectrometry (TG–MS) and Fourier transform infrared (FT-IR) spectroscopy. The results showed that the IEC of composite membrane increased with the content of S-ZrO 2, S-ZrO 2 was compatible with the Nafion matrix, the incorporation of the S-ZrO 2 could increase the crystallinity and also improve the initial degradation temperature of the composite membrane. The performance of single cell was the best when the S-ZrO 2 content was 15 wt.%, and achieved 1.35 W/cm 2 at 80 °C and 0.99 W/cm 2 at 120 °C based on H 2/O 2 and at a pressure of 2 atm, the performance of the single cell with optimized S-ZrO 2 was far more than that of the Nafion at the same condition (e.g. 1.28 W/cm 2 at 80 °C, 0.75 W/cm 2 at 120 °C). The 15 wt.% S-ZrO 2/Nafion composite membrane showed lower fuel cell internal resistance than Nafion membranes at high temperature and low relative humidity (RH). 相似文献
17.
Dichlorobis(3-hydroxi-2-methyl-4-pyrone)Ti(IV) complex was grafted on different inorganic supports, namely different kinds of SiO 2, MAO-modified silica, MCM-41, Al 2O 3, ZrO 2 and MgO. The resulting supported catalysts were shown to be active in ethylene polymerization using methylaluminoxane (MAO) as cocatalyst, most of them being even more active that the homogeneous complex. The highest catalyst activities were observed for the Ti complex supported on SiO 2 948 activated at 450 °C, MCM-41 and Al 2O 3. 相似文献
18.
The solid–liquid equilibria of the ternary system H 2O–Fe(NO 3) 3–Co(NO 3) 2 were studied by using a synthetic method based on conductivity measurements. Two isotherms were established at 0 and 15 °C, and the stable solid phases which appear are the iron nitrate nonahydrate (Fe(NO3)3·9H2O), the iron nitrate hexahydrate (Fe(NO3)3·6H2O), the cobalt nitrate hexahydrate (Co(NO3)2·6H2O) and the cobalt nitrate trihydrate (Co(NO3)2·3H2O). 相似文献
19.
The effects of doping of Co 3O 4with MgO (0.4–6 mol%) and V 2O 5 (0.20–0.75 mol%) on its surface and catalytic properties were investigated using nitrogen adsorption at −196°C and decomposition of H 2O 2 at 30–50°C. Pure and doped samples were prepared by thermal decomposition in air at 500–900°C, of pure basic cobalt carbonate and basic carbonate treated with different proportions of magnesium nitrate and ammonium vanadate. The results revealed that, V 2O 5 doping followed by precalcination at 500–900°C did not much modify the specific surface area of the treated Co 3O 4 solid. Treatment of Co 3O 4 with MgO at 500–900°C resulted in a significant increase in the specific surface area of cobaltic oxide. The catalytic activity in H 2O 2 decomposition, of Co 3O 4 was found to suffer a considerable increase by treatment with MgO. The maximum increase in the catalytic reaction rate constant ( k) measured at 40°C on Co 3O 4 due to doping with 3 mol% MgO attained 218, 590 and 275% for the catalysts precalcined at 500, 700 and 900°C, respectively. V 2O 5-doping of Co 3O 4 brought about a significant progressive decrease in its catalytic activity. The maximum decrease in the reaction rate constant measured at 40°C over the 0.75 mol% V 2O 5-doped Co 3O 4 solid attained 68 and 93% for the catalyst samples precalcined at 500 and 900°C, respectively. The doping process did not modify the activation energy of the catalyzed reaction but much modified the concentration of catalytically active constituents without changing their energetic nature. MgO-doping increased the concentration of CO 3+–CO 2+ ion pairs and created Mg 2+–CO 3+ ion pairs increasing thus the number of active constituents involved in the catalytic decomposition of H 2O 2. V 2O 5-doping exerted an opposite effect via decreasing the number of CO 3+–CO 2+ ion pairs besides the possible formation of cobalt vanadate. 相似文献
20.
The liquid-phase alkylation of phenol with 1-dodecene was carried out over WO x/ZrO 2 solid acid catalysts. The catalysts were prepared by wet impregnation method using zirconium oxyhydroxide and ammonium metatungstate. Catalysts with different WO 3 loading (5–30 wt.%) were prepared and calcined at 800 °C and catalyst with 15% WO 3 was calcined from 700–850 °C. All the catalysts were characterized by surface area, XRD, and FTIR. The catalyst with 15% WO 3 calcined at 800 °C (15 WZ-800) was found to be the most active in the reaction. The effect of temperature, molar ratio and catalyst weight on dodecene conversion and products selectivity was studied in detail. Under the optimized reaction conditions of 120 °C, phenol/1-dodecene molar ratio 2 and time 2 h, the catalyst 15 WZ-800 gave >99% dodecene conversion with 90% dodecylphenol selectivity. Comparison of the catalytic activity of 15 WZ-800 with sulfated zirconia calcined at 500 °C (SZ-500) and Hβ zeolite showed that activity of SZ-500 was lower than that of 15 WZ-800, while Hβ zeolite showed negligible activity. It is observed that the presence of water in the reaction mixture was detrimental to the catalytic activity of WO x/ZrO 2. The catalyst 15 WZ-800 also found to be an efficient catalyst for alkylation of phenol with long-chain olefins like 1-octene and 1-decene. 相似文献
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