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91.
Utilising a pseudo-reference electrode in polymer electrolyte fuel cells allows for the separation of anodic and cathodic contributions to the entire cell impedance. Modelling the impedance responses by using equivalent circuits inhibits the investigation of kinetic parameters of the basic electrochemical reactions, which take place at single electrode-electrolyte interfaces. Therefore, we evaluate single electrode impedance measurements by a kinetic model, which is based on specific reaction pathways, either for the oxygen reduction reaction (ORR) or the hydrogen oxidation reaction (HOR). As a consequence, it is possible to obtain kinetic parameters for the specific reaction of interest. Furthermore, the information gained from the single electrode impedance measurements and the kinetic model can give insight into single reactions steps. In particular, the ORR has to include a chemical step in the reaction pathway. 相似文献
92.
贫燃条件下汽车尾气净化催化技术的发展与展望 总被引:1,自引:0,他引:1
本文介绍了用于贫燃发动机尾气,柴油机尾气净化催化技术的发展状况,对各种催化剂及其载体材料的性能进行了比较,提出了开发贫燃条件汽车尾气净化催化技术尚需解决的问题。 相似文献
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95.
A self-assembled monolayer (SAM) of a novel cobalt(II)porphyrin disulphide derivative was prepared on flat gold(1 1 1) electrode. Evidence for surface modification was provided by electrochemical reductive desorption of the monolayer and ellipsometry, consistent with a coverage of 2.5 × 10−10 mol cm−2 and a thickness of 13 Å, respectively. Both results support the presence of SAMs where the molecules share an intermediate position between perpendicular and flat orientation. Scanning tunnelling microscopy have also proven the formation of CoPSS SAMs, however high-resolution images could only be obtained when the CoPSS molecules were diluted in an hexanethiol SAM. The electrocatalytic activity of the surface confined Co-porphyrin was evaluated for the oxygen reduction. Voltammetric data indicate that reaction involves two electrons consistent with the formation of hydrogen peroxide. Under similar experimental conditions the data obtained for an iron-porphyrin analogue points for a full reduction of dioxygen to water. 相似文献
96.
Direct nitric oxide decomposition over perovskites is fairly slow and complex, its mechanism changing dramatically with temperature. Previous kinetic study for three representative compositions (La0.87Sr0.13Mn0.2Ni0.8O3−δ, La0.66Sr0.34Ni0.3Co0.7O3−δ and La0.8Sr0.2Cu0.15Fe0.85O3−δ) has shown that depending on the temperature range, the inhibition effect of oxygen either increases or decreases with temperature. This paper deals with the effect of CO2, H2O and CH4 on the nitric oxide decomposition over the same perovskites studied at a steady-state in a plug-flow reactor with 1 g catalyst and total flowrates of 50 or 100 ml/min of 2 or 5% NO. The effect of carbon dioxide (0.5–10%) was evaluated between 873 and 923 K, whereas that of H2O vapor (1.6 or 2.5%) from 723 to 923 K. Both CO2 and H2O inhibit the NO decomposition, but inhibition by CO2 is considerably stronger. For all three catalysts, these effects increase with temperature. Kinetic parameters for the inhibiting effects of CO2 and H2O over the three perovskites were determined. Addition of methane to the feed (NO/CH4=4) increases conversion of NO to N2 about two to four times, depending on the initial NO concentration and on temperature. This, however, is still much too low for practical applications. Furthermore, the rates of methane oxidation by nitric oxide over perovskites are substantially slower than those of methane oxidation by oxygen. Thus, perovskites do not seem to be suitable for catalytic selective NO reduction with methane. 相似文献
97.
Controlled calcination of ion-exchanged Wyoming Bentonite in the presence and absence of ammonia leads to layer charge reductions. Detailed chemical analyses of both unexchangeable and exchangeable species lead to the conclusion that in no case is there migration of the original interlamellar cations into the octahedral region of the layers although, in terms of ionic radius alone, Mg2+, Ni2+ and, possibly Co2+, might be expected to do so. The production of unexchangeable Mg, Ni or Co, is identified as resulting from high temperature hydrolysis leading to hydroxide or oxide formation. 相似文献
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99.
Masaru Takahashi Tetsu Nakatani Shinji Iwamoto Tsunenori Watanabe Masashi Inoue 《Applied catalysis. B, Environmental》2007,70(1-4):73-79
The solvothermal reaction of mixtures of aluminum isopropoxide (AIP) and gallium acetylacetonate (Ga(acac)3) directly yielded the mixed oxides of γ-Ga2O3-Al2O3. In the solvothermal synthesis, the crystal structure of mixed oxides was controlled by the initial formation of γ-Ga2O3 nuclei. The mixed oxides prepared in diethylenetriamine have extremely high activities for selective catalytic reduction (SCR) of NO with methane as a reducing agent. With increasing crystallite size of the spinel structure, the catalytic activity increased. The ratio of the amount of methane consumed by combustion to total methane conversion was proportional to the density of acid sites on the surface of the mixed oxides. The mixed oxide catalysts prepared in diethylenetriamine had lower densities of acid sites and showed a higher methane-efficiency for CH4-SCR than those prepared in other solvents. These catalysts maintained their high activity even when the reaction was carried out under the severe conditions (i.e., high space velocity and low NO concentration). 相似文献
100.