共查询到20条相似文献,搜索用时 15 毫秒
1.
《Journal of power sources》2006,159(1):107-110
Hydrogen sorption kinetics of ball milled MgH2 with and without chemical additives were studied. We observed kinetics and capacity improvement with increasing the number of sorption cycles that contributed to the micro/nano cracking of MgH2 particles, shown by XRD and SEM studies. In addition, to investigate the proposed specific role of O2−-based additives on the sorption kinetics of MgH2, we have undertaken a comparative study evaluating the performances of MgH2 containing the NbCl5, CaF2 or Nb2O5 additives. At 300 °C, addition of NbCl5 and CaF2 improved the sorption capacity to 5.2 and 5.6 wt% within 50 min, respectively, in comparison to the required 80 min in the case of Nb2O5. This suggests the importance of the chemical nature of the catalyst for hydrogen sorption in MgH2. In addition, the catalyst specific surface area was shown to be very critical. High surface area Nb2O5 (200 m2 g−1), prepared by novel precipitation method, exhibits an excellent catalytic activity and helped to desorb 4.5 wt% of hydrogen from MgH2 within 80 min at a temperature as low as 200 °C. 相似文献
2.
Ethanol is one of the most important renewable biofuels contributing to the reduction of negative environmental impacts generated by the worldwide utilization of fossil fuels, and the presence of metal ions in fuel ethanol has significant effect on the performance and the quality of fuel. In the present work, silica gel functionalized by poly(triethylenetetraminomethylenephosphonic acid) SG-Cl-T-P was successfully developed by heterogenous synthesis method, and the adsorption capacity of Hg(II) from fuel ethanol via SG-Cl-T-P was examined. The adsorption isotherms were fitted by the Langmuir model, the Freundlich model and the Dubinin–Radushkevich (D–R) model. Furthermore, the adsorption study was analyzed kinetically. The thermodynamic parameters, including the Gibbs free energy change (ΔG), enthalpy change (ΔH) and entropy change (ΔS) were calculated, they were −3.24 kJ mol−1 (35 °C) , 29.25 kJ mol−1, and 106.20 J K−1 mol−1, respectively. 相似文献
3.
The kinetics of oxidation of three soots, from a Diesel engine fuelled by either Ultra-Low Sulphur Diesel (ULSD) or biodiesel, by NO2 have been measured in a packed bed at various temperatures (300–550 °C) and [NO2] (20–880 ppm) relevant to regenerating a Diesel Particulate Filter. Adsorbed hydrocarbons and oxygen accounted for a significant fraction (~20% by mass) of the otherwise carbonaceous material. After pre-treatment (heating up to 550 °C in a flow of pure Ar and holding the temperature at 550 °C for 1 h) to ensure consistency between samples, they were subsequently burned at a fixed temperature in a flow of NO2 + Ar. For this, a balance on oxygen atoms entering and leaving the packed bed showed that during oxidation in NO2 any oxygen remaining in a soot after pre-treatment was not rapidly liberated as CO or CO2. A mass balance on the element nitrogen demonstrated that no N2 or N2O was formed below 550 °C; mass balances on carbon and oxygen demonstrated that all the carbon ended up as CO or CO2 and below 550 °C the nitrogen yielded only NO. The oxidation of soot in NO2 was found to be first-order with respect to NO2. Also, the soot derived from biodiesel was more reactive than soot from ULSD; nevertheless, the apparent activation energies for oxidation by NO2 were the same (70 ± 18 kJ mol?1) for each carbon. When the distribution of diameters of the individual spherules of soot was taken into account, it was not possible to tell whether there was internal burning of porous spherules or, on the other hand, non-porous, solid spherules were burning on their exteriors. 相似文献
4.
Marco Aurélio Bazelatto Zanoni Henrique Massard Márcio Ferreira Martins 《Combustion and Flame》2012,159(10):3224-3234
Enhanced technologies from oil recovery to unconventional fuels - oil shale, oil sands and extra-heavy oil – have in common complex chemical reactions processes. This paper is about the formulation and optimization of the chemical mechanism especially in oil shale and semi-coke combustion. The Levenberg–Marquardt algorithm was used to minimize the error between estimated values and the thermogravimetric data for combustion mechanisms of 4-steps and 3-steps proposed for the oil shale and its semi-coke respectively. The kinetic parameters such as reaction order, pre-exponential factor, activation energy and stoichiometric coefficients that affect drying, pyrolysis, oxidation and decarbonation reactions were estimated with success. The values of activation energies were 54–67 kJ mol?1 for oil shale drying, 62–65 kJ mol?1 for pyrolysis reaction, up to 100 kJ mol?1 for Fixed Carbon (FC) oxidation reaction, and 162–418 kJ mol?1 for decarbonation reaction. Regarding to the semi-coke combustion, the activation energies were 33 kJ mol?1 for drying reaction, 211 kJ mol?1 for oxidation reaction and 291 kJ mol?1 for decarbonation reaction. The chemical reactions suggest reaction order superior to one, except to the decarbonation reaction at 3 K min?1. Considering the estimated parameters, as well as a heating rate at 3 K min?1, an oil shale containing about 20 wt.% of organic matter and 34.6 wt.% of CaCO3, the species mass fractions formed during combustion process were 3.4 wt.% of FC, 10.6 wt.% of Oil, 3.3 wt.% of HC and 1.8 wt.% of CO. The fraction of CO2 formed accounts a total of 21.6 wt.%. For a semi-coke containing 3.4 wt.% of FC and 40.6 wt.% of CaCO3, its combustion formed 2.1 wt.% of CO. The CO2 fraction from oxidation and decarbonation reactions accounts 10.2 wt.%, considering that the stoichiometric mass coefficient γ = 0.75 in decarbonation reaction. 相似文献
5.
This paper presents the study of the transesterification of palm oil via heterogeneous process using montmorillonite KSF as heterogeneous catalyst. This study was carried out using a design of experiment (DOE), specifically response surface methodology (RSM) based on four-variable central composite design (CCD) with α (alpha) = 2. The transesterification process variables were reaction temperature, x1 (50–190 °C), reaction period, x2 (60–300 min), methanol/oil ratio, x3 (4–12 mol mol?1) and amount of catalyst, x4 (1–5 wt%). It was found that the yield of palm oil fatty acid methyl esters (FAME) could reach up to 79.6% using the following reaction conditions: reaction temperature of 190 °C, reaction period at 180 min, ratio of methanol/oil at 8:1 mol mol?1 and amount of catalyst at 3%. 相似文献
6.
《Geothermics》2005,34(1):61-97
Pressure parameters are added to the Extended UNIQUAC model presented by Thomsen and Rasmussen (Modeling of vapor–liquid–solid equilibrium in gas–aqueous electrolyte systems. Chemical Engineering Science 54, 1787–1802, 1999). The improved model has been used for correlation and prediction of solid–liquid equilibrium (SLE) of scaling minerals (CaSO4, CaSO4·2H2O, BaSO4 and SrSO4) at temperatures up to 300 °C and pressures up to 1000 bar. The results show that the Extended UNIQUAC model, with the proposed pressure parameters, is able to represent binary, ternary and quaternary solubility data within the experimental accuracy in the temperature range from −20 to 300 °C, and the pressure range from 1 to 1000 bar. 相似文献
7.
《Journal of power sources》2001,92(1-2):95-101
Lithium cobalt oxide powders have been successfully prepared by a molten-salt synthesis (MSS) method using a eutectic mixture of LiCl and Li2CO3 salts. The physico-chemical properties of the lithium cobalt oxide powders are investigated by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), particle-size analysis and charge–discharge cycling. A lower temperature and a shorter time (∼700°C and 1 h) in the Li:Co=7 system are sufficient to prepare single-phase HT-LiCoO2 powders by the MSS method, compared with the solid-state reaction method. Charge–discharge tests show that the lithium cobalt oxide prepared at 800°C has an initial discharge capacity as high as 140 mA h g−1, and 100 mA h g−1 after 40 cycles. The dependence of the synthetic conditions of HT-LiCoO2 on the reaction temperature, time and amount of flux with respect to starting oxides is extensively investigated. 相似文献
8.
9.
《International Journal of Hydrogen Energy》2019,44(55):29196-29202
The influences of Nb-containing oxides and ternary compound in hydrogen sorption performance were investigated. As faster desorption kinetic and lower activation energy were reported by addition of a ternary compound catalyst such as K2NiF6, the influence of KNbO3 on hydrogen storage properties of MgH2 has been investigated for the first time. The MgH2 - KNbO3 composite desorbed 3.9 wt% of hydrogen within 10 min, while MgH2 and MgH2-Nb₂O₅ composites desorbed 0.66 wt% and 3.2 wt% respectively under similar condition. For MgH2 with other Nb-contained catalysts such as Nb, NbO and Nb₂O3, the desorption rate was almost the same as the one registered for as-milled MgH2. The analysis of differential scanning calorimetry (DSC) showed that MgH2-KNbO3 composite started to release hydrogen at ∼335 °C which is 50 °C lower compared to as-milled MgH2 without any additives. The activation energy for the hydrogen desorption was estimated to be about 104 ± 6.8 kJ mol−1 for this material, while for the as-milled MgH2 was about 165 ± 2.0 kJ mol−1. It is believed that Nb-ternary oxide catalyst (KNbO3) showed a good catalytic effect and enhance the sorption kinetics of MgH2. 相似文献
10.
《Journal of power sources》2006,161(1):40-46
Sintered pellets of Ce-doped Ba2In2O5 (BIC) were prepared from nanopowders. The electrical conductivities were measured using ac impedance spectroscopy under different atmospheres and temperatures. The electrical conductivity of sintered BIC was found sensitive to environmental humidity when the temperature was below 300 °C. However, in the presence of hydrogen, the electrical conductivities were independent of water content in the range of 0–30 vol%. The electrical conductivities of BIC were significantly affected by the presence of hydrogen in a temperature range of 100–300 °C. The estimated protonic transference number and the measured open circuit voltage suggested the existence of electronic conduction. The coefficient of thermal expansion of BIC is 11.2 × 10−6 K−1 from 25 to 1250 °C. 相似文献
11.
《Journal of power sources》2006,161(2):1002-1011
This paper provides a comparative evaluation of electrocatalyst surface area stability in PEM fuel cells under accelerated durability testing. The two basic electrocatalyst types are conventional carbon-supported dispersed Pt catalysts (Pt/C), and nanostructured thin film (NSTF) catalysts. Both types of fuel cell electrocatalysts were exposed to continuous cycling between 0.6 and 1.2 V, at various temperatures between 65 and 95 °C, with H2/N2 on the anode and cathode, while periodic measurements of electrochemical surface area were recorded as a function of the number of cycles. The NSTF electrocatalyst surface areas were observed to be significantly more stable than the Pt/C electrocatalysts. A first order rate kinetic model was applied to the normalized surface area changes as a function of number of cycles and temperature, and two parameters extracted, viz. the minimum stable surface area, Smin, and the activation energy, Ea, for surface area loss in this voltage range. Smin was found to be 10% versus 66%, and Ea 23 kJ mole−1 versus 52 kJ mole−1, for Pt/C versus NSTF-Pt, respectively. The loss of surface area in both cases is primarily the result of Pt grain size increases, but the Pt/C XRD grain sizes increase significantly more than the NSTF grain sizes. In addition, substantial peak shifts occur in the Pt/C CVs, which ultimately end up aligning with the NSTF peak positions, which do not change substantially due to the voltage cycling. NSTF catalysts should be more robust against shut down/start-up, operation near OCV and local H2 starvation effects. 相似文献
12.
《Journal of power sources》2006,158(1):137-142
Sulfonic-functionalized heteropolyacid–SiO2 nanoparticles were synthesized by grafting and oxidizing of a thiol-silane compound onto the heteropolyacid–SiO2 nanoparticle surface. The surface functionalization was confirmed by solid-state NMR spectroscopy. The composite membrane containing the sulfonic-functionalized heteropolyacid–SiO2 nanoparticles was prepared by blending with Nafion® ionomer. TG–DTA analysis showed that the composite membrane was thermally stable up to 290 °C. The DMFC performance of the composite membrane increased the operating temperature from 80 to 200 °C. The function of the sulfonic-functionalized heteropolyacid–SiO2 nanoparticles was to provide a proton carrier and act as a water reservoir in the composite membrane at elevated temperature. The power density was 33 mW cm−2 at 80 °C, 39 mW cm−2 at 160 °C and 44 mW cm−2 at 200 °C, respectively. 相似文献
13.
《Journal of power sources》2006,159(1):163-166
Mg–Ce alloy was prepared by induction melting under vacuum, hydrided firstly and then Mg–Ce/Ni composite was obtained by mechanical milling Mg–Ce hydrides under Ar for 50 h with addition of nano-sized Ni powder. XRD results showed CeMg12 formed in melted alloy. CeMg12 disappeared and CeH2.53 emerged during subsequent hydriding. The phase composition was not changed during ball milling process. Compared with Mg and Mg/Ni, Mg–Ce/Ni composite showed significant hydriding/dehydriding performance without any prior activation. The enthalpy of hydride formation for Mg–10.9 wt.% Ce/10 wt.% Ni composite was −70.58 kJ mol−1 H2. Improved hydrogen storage properties were attributed to the catalytic effect of addition of nano-sized Ni particles and existence of CeH2.53, as well as the grain refinement, defects, etc. in the material introduced by ball milling process. 相似文献
14.
《Journal of power sources》2006,159(1):365-369
Thin nickel oxide (NiO) films were obtained by post-heating of the corresponding precursor films of nickel hydroxide (Ni(OH)2) cathodically deposited onto different substrates, i.e., nickel foils, and graphite at 25 °C from a bath containing 1.5 mol L−1 Ni(NO3)2 and 0.1 mol L−1 NaNO3 in a solvent of 50% (v/v) ethanol. The surface morphology of the obtained films was observed by scanning electron microscope (SEM). Electrochemical characterization was performed using cyclic voltammetrty (CV), chronopotentiometry (CP) and electrochemical impedance analysis (EIS). When heated at 300 °C for 2 h in air, the specific capacitance of the prepared NiO films on nickel foils and graphite, with a deposition charge of 250 mC cm−2, were 135, 195 F g−1, respectively. When the deposition charge is less than 280 mC cm−2, the capacitance of both appears to keep the linear relationship with the deposition charge. The specific capacitance, cyclic stability of the NiO/graphite hybrid electrodes in 1 mol L−1 KOH solution were superior to those on nickel foils mainly due to the favorable adhesion, the good interface behavior between graphite and the NiO films, and the extra pseudo-capacitance of the heated graphite substrates. 相似文献
15.
《Journal of power sources》2007,164(2):496-502
The hydrogen storage performances of the Li–Mg–N–H system are investigated starting either from 1:2 Mg(NH2)2–LiH or 1:2 MgH2–LiNH2 ball-milled mixtures. It is shown that, for 1:2 MgH2–LiNH2, an ammonia release occurs if the first heating is conducted under a dynamic vacuum, leading to a fast degradation of the material. The positive role of LiH, if initially present in the mixture, is therefore emphasized as LiH rapidly reacts with ammonia and avoids the contamination of the hydrogen desorbing flow. The desorption kinetics of the ball-milled 1:2 Mg(NH2)2–LiH mixture are fast: a total amount of 5.0 wt.% of hydrogen is desorbed in 25 min at 220 °C. This material exhibits a nice reversibility at 200 °C with an experimental capacity around 4.8 wt.%. Preliminary results are given on the structure of Li2Mg(NH)2, formed upon desorption: this phase crystallizes in a cubic unit cell with a lattice parameter of 10.06(1) Å. In addition, by plotting an absorption isotherm of the Li2Mg(NH)2 phase at 200 °C, two pressure plateaus are observed revealing the existence of an intermediary phase between Li2Mg(NH)2 and the rehydrided material, which is the 1:2 Mg(NH2)2–LiH mixture. 相似文献
16.
《Journal of power sources》2006,153(1):174-176
LiNi0.5Mn1.5O4 was prepared by an improved solid-state reaction at high heating and cooling rates, the mixed precursors were initially heated up to 900 °C, then directly cooled down to 600 °C and heated for 24 h in air. X-ray diffraction (XRD) pattern shows that LiNi0.5Mn1.5O4 has cubic spinel structure; scanning electron microscopic (SEM) image shows that the particle size is about 0.2 μm together with homogenous distribution. Electrochemical measurements show that LiNi0.5Mn1.5O4 powders delivered up to 143 mAh g−1 with superior cycling performance at the rate of 5/7C. 相似文献
17.
Thermogravimetric (TG) analysis was used to study and compare the combustion of sewage sludge (SS), animal manure (AM) and the organic fraction of municipal solid waste (OFMSW). TG curves are in correspondence with the volatiles and carbon content of the materials studied. Non-isothermal thermogravimetric data were used to assess the kinetics of the combustion of these carbonaceous materials. The paper reports on the application of a model-free isoconversional method for the evaluation of the activation energy corresponding to the combustion of these biowastes. The activation energy related to AM combustion (E ~ 140 kJ mol?1) was similar to that corresponding to SS (E ~ 143 kJ mol?1) while the OFMSW showed to have a higher value (E ~ 173 kJ mol?1). 相似文献
18.
Boron-doped hydrogenated microcrystalline silicon oxide (p-μc-Si:Ox:H) films have been deposited using catalytic chemical vapor deposition (Cat-CVD). The single-coiled tungsten catalyst temperature (Tfil) was varied from 1850 to 2100 °C and films were deposited on glass substrates at the temperatures (Tsub) of 100–300 °C. Different catalyst-to-substrate distances of 3–5 cm and deposition pressures from 0.1 to 0.6 Torr were considered.Optical and electrical characterizations have been made for the deposited samples. The sample transmittance measurement shows an optical-bandgap (Egopt) variation from 1.74 to 2.10 eV as a function of the catalyst and substrate temperatures. One of the best window materials was obtained at Tsub=100 °C and Tfil=2050 °C, with Egopt=2.10 eV, dark conductivity of 3.0×10?3 S cm?1 and 0.3 nm s?1 deposition rate. 相似文献
19.
《Journal of power sources》2006,160(1):73-77
Tubular SOFC systems appear to be well-suited to accommodate repeated cycling under rapid changes in electrical load and in cell operating temperatures. Our goal is to develop innovative processing method to fabricate new micro tubular SOFCs with sub-millimeter diameter and its stack module which enable to generate high volumetric power density. In this study, micro tubular SOFCs under 1 mm diameter have been successfully fabricated and tested in the intermediate temperature region (550 °C or under). The cell consists of NiO–Gd doped ceria (GDC) as an anode (support tube), GDC as an electrolyte and (La, Sr)(Fe, Co)O3 (LSCF)–GDC as a cathode. The single tubular cell with 0.8 mm diameter and 12 mm length generated over 70 mW at 550 °C with H2 fuel, which indicates that the cell generated over 0.3 W cm−2 at 550 °C. 相似文献
20.
《Journal of power sources》2006,154(2):394-403
Electrical output behaviour obtained on solid oxide fuel cell stacks, based on planar anode supported cells (50 or 100 cm2 active area) and metallic interconnects, is reported. Stacks (1–12 cells) have been operated with cathode air and anode hydrogen flows between 750 and 800 °C operating temperature. At first polarisation, an activation phase (increase in power density) is typically observed, ascribed to the cathode but not clarified. Activation may extend over days or weeks. The materials are fairly resistant to thermal cycling. A 1-cell stack cycled five times in 4 days at heating/cooling rates of 100–300 K h−1, showed no accelerated degradation. In a 5-cell stack, open circuit voltage (OCV) of all cells remained constant after three full cycles (800–25 °C). Power output is little affected by air flow but markedly influenced by small fuel flow variation. Fuel utilisation reached 88% in one 5-cell stack test. Performance homogeneity between cells lay at ±4–8% for three different 5- or 6-cell stacks, but was poor for a 12-cell stack with respect to the border cells. Degradation of a 1-cell stack operated for 5500 h showed clear dependence on operating conditions (cell voltage, fuel conversion), believed to be related to anode reoxidation (Ni). A 6-cell stack (50 cm2 cells) delivering 100 Wel at 790 °C (1 kWel L−1 or 0.34 W cm−2) went through a fuel supply interruption and a thermal cycle, with one out of the six cells slightly underperforming after these events. This cell was eventually responsible (hot spot) for stack failure. 相似文献