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1.
The thermodynamic analysis and the results of thermogravimetric investigation of the reduction of magnesium sulfate by carbon oxide are reported.The isothermal experiments were carried out in the temperature range 640 to 675°. A shrinking-core model was found to fit the reaction rate. An activation energy of 209.7±8.6 kJ/mol was obtained.
Zusammenfassung Es wird über thermodynamische Analyse und Resultate einer thermogravimetrischen Untersuchung der Reduktion von Magnesiumsulfat mit Kohlendioxid berichtet. Die isothermen Experimente wurden im Temperaturbereich 640 bis 675° durchgeführt. Zur Erklärung der Reaktionsgeschwindigkeit wurde eine Shrinking-Modell gefunden. Es wurde eine Aktivierungsenergie von 209.7±8.6 kJ/mol erhlten.
. 640–675°. , . 209,7±8,6 /.相似文献
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Reduction kinetics of magnesia with carbon powder was studied using the thermal gravimetric technic in the temperature range of 1743–1883 K. The reduction ratio was determined as a function of time. The effects of compact-forming pressure, composition, partial pressure of CO, sample height, and temperature on reduction ratio were investigated. Experimental results revealed that the gas diffusion including Mg vapor, CO and CO2 through the porous medium was the rate-determining step of the overall reduction process. Activation energy of the gas diffusion was estimated to be about 30.59 kJ mol−1. 相似文献
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The non-isothermal reductive decomposition reaction of crystalline CaSO3·0.5H2O and anhydrous CaSO3 under CO, CO2 and CO-CO2 gas mixtures at the two heating rates of 25°C min−1 and 6°C min−1 up to 900°C, respectively, was investigated employing thermogravimetric analysis, X-ray powder diffraction, IR spectroscopy and continuous SO2 measurement by on-line fluorescence spectroscopy. During the heating process the reaction involved a multistage weight loss, in both cases, with a corresponding multistage SO2 release. The multistage weight loss and the corresponding SO2 release were presumed to be the consequence of different sequential reactions taking place along with the direct reduction of CaSO3 to CaS, including the formation and decomposition of CaCO3 and CaSO4, respectively. The corresponding SO2 evolution was found to be considerably lower at slow heating rates. In the presence of additional CO2, the SO2 release was increased and the highest SO2 concentration was found for a feed-gas mixture of 70% CO2 and 30% CO, and also in pure CO2. The CaCO3 product also increased with increasing CO2 concentration. The possible reaction pathway is discussed. 相似文献
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A. v. Richthofen E. Wendel D. Neuschütz 《Fresenius' Journal of Analytical Chemistry》1993,346(1-3):261-264
Summary The kinetics of the reduction of nitric oxide with pure and potassium-doped carbon, NO+C=1/2 N2+CO, were investigated. For the reaction of NO with pure carbon, measurements were made in the temperature range from 1750 K to 2130 K and at initial NO pressures between 5×10–3 Pa and 7×10–2 Pa. The reaction was first order with respect to nitric oxide at NO pressures below 3×10–2 Pa. The activation energy was 54 kJ/mol for temperatures below 2000 K, while at higher temperatures a second (parallel) reaction became noticeable with a definitely higher activation energy. Potassium-doped carbon was prepared by a molecular beam technique. AES studies verified that potassium was intercalated into the graphite surface and that the potassium-to-carbon ratio changed continuously with sample temperature. The reduction of NO with K-doped carbon was investigated in the temperature range from 710 K to 1080 K and at initial NO pressures between 7×10–5 Pa and 6×10–4 Pa while monitoring, in-situ using AES the K/C-ratio of the surface. The NO reduction rate rose linearly with K/C. Compared to pure carbon, the reaction rate for the NO reduction with K-doped carbon increased by a factor in the range of 104. The activation energy for the NO reduction with K-doped carbon was found to be 82 kJ/mol. 相似文献
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Xueni Zhao Hejun Li Mengdi Chen Kezhi Li Jinhua Lu Leilei Zhang Sheng Cao 《Surface and interface analysis : SIA》2012,44(1):21-28
Nano/micro‐sized calcium phosphate (CaP) coating was prepared on carbon/carbon (C/C) composites by ultrasonic assisted electrochemical deposition. The coating obtained at different deposition voltages contained a mixture of hydroxyapatite (HA) and brushite (DCPD). The homogenous coating prepared at 2.4 V consisted of nano‐sized and needle‐like HA embedded in micro‐sized and plate‐like DCPD. An interlocking structure was formed along the depth direction of the coating. The internal stress may be released effectively through the interlocking structure of the coating. And the plate‐like crystals of the coating were inset in the grooves on the surface of C/C composites. This led to a better adhesive strength of the coating. Meanwhile, the formed interlocking structure could help enhance cohesive strength of the coating. It was found that the growth of CaP crystals in the coating under the voltage of 2.4 V consisted of the plate‐like crystals deposited initially. Then the plate‐needle‐like crystals of submicron size formed among the plate‐like crystals and developed needle‐like ones. The CaP‐coated C/C composites might improve the biological properties of coating for its unique morphology, structures and strong adhesion to the C/C substrate. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
9.
The effects of Co alloying to Pt catalyst and Nafion pretreatment by NaClO4 solution on the rate-determining step (RDS) of oxygen reduction at Nafion-impregnated Pt-dispersed carbon (Pt/C) electrode
were investigated as a function of the potential step ΔE employing potentiostatic current transient (PCT) technique. For this purpose, the cathodic PCTs were measured on the pure
Nafion-impregnated and partially Na+-doped Nafion-impregnated Pt/C and PtCo/C electrodes in an oxygen-saturated 1 M H2SO4 solution and analyzed. From the shape of the cathodic PCTs and the dependence of the instantaneous current on the value of
ΔE, it was confirmed that oxygen reduction at the pure Nafion-impregnated electrodes is controlled by charge transfer at the
electrode surface mixed with oxygen diffusion in the solution below the transition potential step |ΔE
tr| in absolute value, whereas oxygen reduction is purely governed by oxygen diffusion above |ΔE
tr|. On the other hand, the RDS of oxygen reduction at the partially Na+-doped Nafion-impregnated electrodes below |ΔE
tr| is charge transfer coupled with proton migration, whereas above |ΔE
tr|, it becomes proton migration in the Nafion electrolyte instead of oxygen diffusion. Consequently, it is expected in real
fuel cell system that the cell performance is improved by Co alloying since the electrode reaches the maximum diffusion (migration)
current even at small value of |ΔE|, whereas the cell performance is aggravated by Nafion pretreatment due to the decrease in the maximum diffusion (migration)
current. 相似文献
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Increasing energy demand in the world leads to more electricity generation mainly at fossil fuel power plants. Greenhouse gases are thus produced and mostly emitted to the atmosphere directly, resulting in global warming and climate change. Carbon dioxide is believed to be a main pollutant among greenhouse gases responsible from global warming. Conventional systems using mostly amine solutions to capture carbon dioxide at the source have some disadvantages, and alternatives are constantly being searched. In this work, a benign system of aqueous calcium acetate solution was investigated for this purpose. Calcium acetate is easy to produce, relatively cheap, environmentally friendly, nonhazardous, and noncorrosive. These properties make it a great alternative for use in capturing carbon dioxide. This absorption process is accompanied by chemical reaction. Therefore, the reaction kinetics needs to be investigated before its use in absorbers. A stirred cell reactor was used in the experiments using aqueous calcium acetate solution of different concentrations (2-20% w/w) and different carbon dioxide concentrations in gas mixtures (4.5-100% v/v dry carbon dioxide) at temperatures ranging from 286 to 352 K. The Gibbs free energy change for the overall reaction between carbon dioxide and aqueous calcium acetate solution was found to be –2.75 kJ/mol that shows the reaction is exergonic and occurs spontaneously. It was also found out that the reaction is pseudo–first order with respect to carbon dioxide which was also proven by calculating the Hatta number. Activation energy and Arrhenius (frequency) constant were also determined experimentally. 相似文献
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Ya. A. Dorfman V. S. Emelyanova B. O. Zhusupbekov 《Reaction Kinetics and Catalysis Letters》1981,16(1):55-60
Kinetic studies of nitric oxide reduction by carbon monoxide in the presence of Co(II) complexes indicate that the reaction is first order with respect to catalyst, carbon monoxide, and nitric, oxide. Co(AC2)(OH)
2
–
complexes have the highest catalytic activity. A reduction mechanism is proposed.
Co(II). , , . Co(Ac2)(OH) 2 – . .相似文献
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T. A. Kravchenko D. V. Konev S. V. Peshkov S. P. Starodubova E. S. Kipriyanova S. V. Khorol’skaya 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2011,85(7):1196-1201
It was experimentally determined that the rate of reduction of molecular oxygen from water by the nanocomposite silver-ion
exchanger KU-23 is substantially lower than by copper-containing composite and takes place with substantial kinetic inhibition.
The kinetic parameters of the process were determined by solving the reverse kinetic problem; it was found that this was due
to a reduction in the rate constant of the reaction of silver with oxygen at virtually constant internal diffusion coefficient
of molecular oxygen. The transition from kinetic to diffusion control was determined to depend on the silver particle size. 相似文献
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Removal of phosphate from solution by adsorption and precipitation of calcium phosphate onto monohydrocalcite 总被引:3,自引:0,他引:3
The sorption behavior and mechanism of phosphate on monohydrocalcite (CaCO3?H2O: MHC) were examined using batch sorption experiments as a function of phosphate concentrations, ionic strengths, temperatures, and reaction times. The mode of PO4 sorption is divisible into three processes depending on the phosphate loading. At low phosphate concentrations, phosphate is removed by coprecipitation of phosphate during the transformation of MHC to calcite. The sorption mode at the low-to-moderate phosphate concentrations is most likely an adsorption process because the sorption isotherm at the conditions can be fitted reasonably with the Langmuir equation. The rapid sorption kinetics at the conditions is also consistent with the adsorption reaction. The adsorption of phosphate on MHC depends strongly on ionic strength, but slightly on temperature. The maximum adsorption capacities of MHC obtained from the regression of the experimental data to the Langmuir equation are higher than those reported for stable calcium carbonate (calcite or aragonite) in any conditions. At high phosphate concentrations, the amount of sorption deviates from the Langmuir isotherm, which can fit the low-to-moderate phosphate concentrations. Speciation–saturation analyses of the reacted solutions at the conditions indicated that the solution compositions which deviate from the Langmuir equation are supersaturated with respect to a certain calcium phosphate. The obtained calcium phosphate is most likely amorphous calcium phosphate (Ca3(PO4)2?xH2O). The formation of the calcium phosphate depends strongly on ionic strength, temperature, and reaction times. The solubility of MHC is higher than calcite and aragonite because of its metastability. Therefore, the higher solubility of MHC facilitates the formation of the calcium phosphates more than with calcite and aragonite. 相似文献
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氯化钙催化纤维素热裂解动力学研究 总被引:12,自引:3,他引:12
用差示热重分析仪对氯化钙纤维素热裂解动力学催化影响进行了研究。结果表明,氯化钙对焦炭的形成具有强烈的促进效果,使热裂解最终残留物产率从5%提升到10%以上,氯化钙的存在影响到热失重初始阶段活性纤维素的生成,使热重曲线向低温侧移动,并在低温段产生了小的失重速率峰。通过热重分析发现,氯化钙催化条件下纤维素热裂解动力学参数被分为了三段,分别对应于活性纤维素的生成、炭化和活性纤维素转化为挥发分产物三个区间,并依次成为整体失重过程的控制步骤。结合Broido-Shafizadeh机理分析以及与纯纤维素热裂解动力学参数的对比,氯化钙对这三个主要反应步骤都产生了促进效果,其中以催化焦炭的生成最为明显,在促进焦炭化的过程中,降低了气体产物的生成比率。 相似文献
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The kinetics of the reaction between γ-Al2O3 and gaseous CCl4 has been studied by isothermal TG measurements in the temperature range 700—1123 K. The reaction starts with a weight gain which can be attributed to the chemisorption of the reactive gas. The weight loss vs. time curves at relatively high temperatures can be described by the contracting cylinder equation and at relatively low temperatures by first-order kinetics. The dependence of the initial reaction rate on the CCl4 partial pressure follows the Langmuir—Hinshelwood rate expression. At 700—723 K, chemical control is thought to be predominant and an apparent activation energy of 212 kJ mole?1 is found for the chlorination process. 相似文献
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A. M. Kalinkin 《Journal of Thermal Analysis and Calorimetry》2009,95(1):105-110
Kinetics of mechanically induced CO2 extensive sorption by silicate minerals (labradorite, diopside, okermanite, ghelenite and wollastonite) was considered. Mechanical
activation of the silicates was carried out in a planetary mill in CO2 at atmospheric pressure. Carbon dioxide was consumed by the silicates in the form of carbonate ions and its content in the
samples after 30 min of mechanical treatment reached 3–12 mass% CO2 depending on mineral composition. Equations that reasonably good represent kinetics of CO2 mechanosorption by silicates were proposed. These equations enable to calculate mechanosorption coefficients that characterize
the diffusivity of CO2 into disordered silicate matrix under intensive mechanical impact. Thermal analysis of the mechanically activated silicates
showed that there was positive correlation between temperature of complete carbonate decomposition and mechanosorption coefficient. 相似文献
19.
Fan He Sirui Tong Zhouyang Luo Haoran Ding Ziye Cheng Chenxi Li Zhifu Qi 《Journal of Energy Chemistry》2023,(4):398-409
Electroreduction of CO2 shows great potential for global CO2 utilization and uptake when collaborated with renewable electricity. Recent advances have been achieved in fundamental understanding and electrocatalyst development for CO2 electroreduction. We think this research area has progressed to the stage where significant efforts can focus on translating the obtained knowledge to the development of largescale electrolyzers, which have the potential to accelerat... 相似文献
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A. S. Berenblyum Hussein Ali Al-Wadhaf E. A. Katsman V. R. Flid 《Kinetics and Catalysis》2011,52(2):296-304
The kinetics of the reduction of Pd(II) compounds by dihydrogen on the surface of a carbon support has been investigated for
palladium acetate as an example. A kinetic model has been constructed for this reaction. An autocatalytic mechanism is suggested,
in which the key role is played by Pd(0) compounds and their hydrides. The reaction occurring on the support surface is compared
with the same reaction in solutions of palladium phosphine acetate complexes, where a similar mechanism is observed. One of
the most important features of the surface reaction is the relatively slow reduction of the Pd(I) compounds to Pd(0). This
makes it possible to obtain materials with a high Pd(I) content of 5% and above. 相似文献