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1.
A series of palladium-substituted La 2CuO 4, corresponding to the formula La 2Cu 1 −xPd xO 4 ( x = 0−0.2) were prepared by metal nitrate decomposition in a polyacrylamide gel. This method allows an easy incorporation of palladium in the mixed-oxides, which are formed at moderate temperature with rather high specific areas (13–17 m 2/g). The partial substitution of copper for palladium allows a strong improvement of the three-way catalytic activity, in particular for NO reduction. The light-off temperatures for the conversions of CO, NO and C 3H 6 decreased markedly when increasing the palladium content, the activity of catalysts La 2Cu 0.9Pd 0.1O 4 and La 2Cu 0.8Pd 0.2O 4 being comparable to that of a Pt-Rh/CeO 2–Al 2O 3 catalyst for NO reduction, and higher for CO and C 3H 6 oxidation. All the La2Cu1 − x PdxO4 catalysts are activated under reacting conditions. This activation corresponds to the destruction of the mixed-oxide structure, with formation of reduced Pd0 ions atomically dispersed, surrounded by Cu+ and Cu2+ species on a lanthanum oxycarbonate matrix. This high dispersion state of the two transition metals in various oxidation states is supposed to originate from the initial La2Cu1 −xPdxO4 structure. 相似文献
2.
采用火焰喷雾合成法制备了Sr 2+、Cu 2+分别取代A、B位的La 0.8Sr 0.2Mn 1-xCu xO 3 ( x=0,0.1,0.2,0.3,0.4)钙钛矿催化剂,并用于CO催化氧化实验,研究了水蒸气和CO 2对催化剂CO氧化活性的影响。对不同取代量La 0.8Sr 0.2Mn 1-xCu xO 3 催化剂进行了XRD、SEM、EDS、BET、XPS、H 2-TPR和O 2-TPD等表征测试。结果表明,火焰喷雾合成法制备的钙钛矿催化剂具有良好的钙钛矿相、疏松多孔结构和催化氧化活性。其中,La 0.8Sr 0.2Mn 0.9Cu 0.1O 3分别在119.4℃和133.3℃实现50%和90%的CO转化率。掺杂水蒸气和CO 2会与CO在催化剂表面形成竞争吸附,导致5种催化剂性能衰减,但La 0.8Sr 0.2Mn 0.9Cu 0.1O 3仍能在150.2℃实现90%的CO催化转化,在连续稳定性催化氧化测试中,5种催化剂性能衰减不超过10%。结合上述CO催化氧化实验,火焰喷雾合成法制备的催化剂具有良好的稳定性和催化活性,适合制备高CO催化氧化活性的钙钛矿催化剂。 相似文献
3.
Direct nitric oxide decomposition over perovskites is fairly slow and complex, its mechanism changing dramatically with temperature. Previous kinetic study for three representative compositions (La 0.87Sr 0.13Mn 0.2Ni 0.8O 3−δ, La 0.66Sr 0.34Ni 0.3Co 0.7O 3−δ and La 0.8Sr 0.2Cu 0.15Fe 0.85O 3−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 CO 2, H 2O and CH 4 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 H 2O vapor (1.6 or 2.5%) from 723 to 923 K. Both CO 2 and H 2O inhibit the NO decomposition, but inhibition by CO 2 is considerably stronger. For all three catalysts, these effects increase with temperature. Kinetic parameters for the inhibiting effects of CO 2 and H 2O over the three perovskites were determined. Addition of methane to the feed (NO/CH 4=4) increases conversion of NO to N 2 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
4.
Ag-modified La 0.6Sr 0.4MnO 3-based catalysts with the perovskite-type structure were prepared by using a citric acid sol–gel method, and their catalytic performance for complete oxidation of methanol and ethanol was evaluated and compared with that of the γ-Al 2O 3-supported catalysts, Ag/γ-Al 2O 3, Pt/γ-Al 2O 3, and Pd/γ-Al 2O 3. The results showed that the Ag-modified La 0.6Sr 0.4MnO 3-based catalysts with the perovskite-type structure displayed the activity significantly higher than that of the supported precious metal catalysts, 0.1%Pd/γ-Al 2O 3 and 0.1%Pt/γ-Al 2O 3 in the temperature range of 370–573 K. Over a 6%Ag/20%La 0.6Sr 0.4MnO 3/γ-Al 2O 3 catalyst, the T95 temperature for methanol oxidation can be as low as 413 K. Even at such low reaction temperature, there were little HCHO and CO detected in the reaction exit-gas. However, for the 0.1%Pd/γ-Al 2O 3 and 0.1%Pt/γ-Al 2O 3 catalysts, the HCHO content in the reaction exit-gas reached 200 and 630 ppm at their T95 temperatures. Over a 6%Ag/La 0.6Sr 0.4MnO 3 catalyst, the T95 temperature for ethanol oxidation can be as low as 453 K, with a corresponding content of CH 3CHO in the exit-gas at 782 ppm; when ethanol oxidation is performed at 493 K, the content of acetaldehyde in the exit-gas can be below 1 ppm. Characterization of the catalysts by X-ray diffraction (XRD), TEM, XPS, laser Raman spectra (LRS), hydrogen temperature-programmed reduction (H 2-TPR) and oxygen temperature-programmed desorption (O 2-TPD) methods revealed that both the surface and the bulk phase of the perovskite La 0.6Sr 0.4MnO 3 played important roles in the catalytic oxidation of the alcohols, and that γ-Al 2O 3 as the bottom carrier could be beneficial in creating a large surface area of catalyst. Moreover, a small amount of Ag + doped onto the surface of La 0.6Sr 0.4MnO 3 was able to partially occupy the positions of La 3+ and Sr 2+ due to their similar ionic radii, and thus, became stabilized by the perovskite lattice, which would be in favor of preventing the aggregation of the Ag species on the surface and enhancing the stability of the catalyst. On the other hand, modification of the Ag + to the surface of La 0.6Sr 0.4MnO 3 resulted in an increase in relative content of the surface O 22−/O − species highly reactive toward the alcohols and aldehydes as well as CO. Besides, solution of low-valence metal oxides SrO and Ag 2O with proper amounts in the lattice of the trivalent metal perovskite-type oxide LaMnO 3 would also lead to an increase in the content of the reducible Mn n+ and the formation of anionic vacancies, which would be favorable for the adsorption-activation of oxygen on the functioning catalyst and the transport of the lattice and surface oxygen species. All these factors would contribute to the pronounced improvement of the catalyst performance. 相似文献
5.
Reduction behavior of pure and doped CeO 2, the multi-phase La 0.6Sr 0.4CoO 3? xCeO 2, La 0.8Sr 0.2MnO 3 ? xCeO 2, and La 0.95Ni 0.6Fe 0.4O 3? xCeO 2 composites, was studied under hydrogen containing atmosphere to address issues related to the improvement of electrochemical and catalytic performance of electrodes in fuel cells. The enhanced reduction of cerium oxide was observed initially at 800°C in all composites in spite of the presence of highly reducible transition metal cations that could lead to the increase in surface concentration of oxygen vacancies and generation of the electron enriched surface. Due to continuous reduction of cerium oxide in La 0.6Sr 0.4CoO 3? xCeO 2 and La 0.8Sr 0.2MnO 3? xCeO 2 (up to 10 h) composites the redox activity of the Ce 4+/Ce 3+ pair could be suppressed and additional measures are required for reversible spontaneous regeneration of Ce 4+. After 3 h exposure to H 2-Ar at 800°C the reduction of cerium oxides and perovskite phases in La 0.95Ni 0.6Fe 0.4O 3? xCeO 2 composites was diminished. The extent of cerium oxide involvement in the reduction process varies with time, and depends on its initial deviation from oxygen stoichiometry (that results in the larger lattice parameter and the longer pathway for O 2- transport through the fluorite lattice), chemical origin of transition metal cations in the perovskite, and phase diversity in multi-phase composites. 相似文献
6.
Mixed oxides of the general formula La 0.5Sr xCe yFeO z were prepared by using the nitrate method and characterized by XRD and Mössbauer techniques. The crystal phases detected were perovskites LaFeO 3 and SrFeO 3−x and oxides -Fe 2O 3 and CeO 2 depending on x and y values. The low surface area ceramic materials have been tested for the NO+CO and NO+CH 4+O 2 (“lean-NO x”) reactions in the temperature range 250–550°C. A noticeable enhancement in NO conversion was achieved by the substitution of La 3+ cation at A-site with divalent Sr +2 and tetravalent Ce +4 cations. Comparison of the activity of the present and other perovskite-type materials has pointed out that the ability of the La 0.5Sr xCe yFeO z materials to reduce NO by CO or by CH 4 under “lean-NO x” conditions is very satisfying. In particular, for the NO+CO reaction estimation of turnover frequencies (TOFs, s −1) at 300°C (based on NO chemisorption) revealed values comparable to Rh/-Al 2O 3 catalyst. This is an important result considering the current tendency for replacing the very active but expensive Rh and Pt metals. It was found that there is a direct correlation between the percentage of crystal phases containing iron in La 0.5Sr xCe yFeO z solids and their catalytic activity. O 2 TPD (temperature-programmed desorption) and NO TPD studies confirmed that the catalytic activity for both tested reactions is related to the defect positions in the lattice of the catalysts (e.g., oxygen vacancies, cationic defects). Additionally, a remarkable oscillatory behavior during O 2 TPD studies was observed for the La 0.5Sr 0.2Ce 0.3FeO z and La 0.5Sr 0.5FeO z solids. 相似文献
7.
氨分解得到的H 2不含CO x 、SO x 、NO x 等有害物质,是其他所有含碳资源为原料制氢所不能比拟的。本文采用无模板水热法制备了一系列棒状载体,并采用沉积沉淀法制备了Ru/La x Ce 1-x O y 催化剂,考察了制备方法、催化剂组成对性能的影响,并通过扫描电镜(SEM)、X射线衍射(XRD)、BET、H 2-程序升温还原(TPR)和CO 2-程序升温脱附(TPD)进行了表征。结果表明,La 2O 3掺杂量为40%的Ru/La 0.4Ce 0.6O 1.8催化剂在常压、7800h -1、450℃下氨分解转化率为98%。该催化剂活性高归因于部分还原的CeO 2-x 对Ru的供电子性能和Ru/La 0.4Ce 0.6O 1.8催化剂表面的强碱性增加了对Ru活性位的给电子能力。同时考察了K 2O含量的影响,最优的催化剂为Ru-2%K/La 0.4Ce 0.6O 1.8,在400℃、7800h -1氨气转化率可以达到93%。结果表明Ru-2%K/La 0.4Ce 0.6O 1.8可以作为一种新型高效氨分解催化剂,为工业化应用提供了可能,具有良好的发展前景。 相似文献
8.
为了提高固体氧化物燃料电池在中温条件下的电性能,探索了一种双金属阳极的阴极支撑单电池。单电池以La 0.6Sr 0.4CoO 3(LSC)-Ce 0.9Gd 0.1O 1.95(GDC)为阴极支撑体,旋涂了甘氨酸-硝酸盐法制备的La 0.9Sr 0.1Ga 0.8Mg 0.2O 3-δ(LSGM)电解质及Sm 0.2Ce 0.8O 1.9(SDC)缓冲层,涂覆了由硬模板法和浸渍法结合制备的Ni-Fe/GDC双金属阳极。对制备材料进行了XRD和微观形貌分析,单电池电化学测试在800 ℃和750 ℃下,以氢气为燃料的最大功率密度达0.73 W/cm 2和0.64 W/cm 2,以甲烷为燃料时达0.41 W/cm 2和0.40 W/cm 2。测试后的SEM表明,阳极具有多孔的微观结构,金属颗粒均匀包覆蠕虫状GDC,保证了单电池具有较高的发电性能。 相似文献
9.
Dispersing La 2O 3 on δ- or γ-Al 2O 3 significantly enhances the rate of NO reduction by CH 4 in 1% O 2, compared to unsupported La 2O 3. Typically, no bend-over in activity occurs between 500° and 700°C, and the rate at 700°C is 60% higher than that with a Co/ZSM-5 catalyst. The final activity was dependent upon the La 2O 3 precursor used, the pretreatment, and the La 2O 3 loading. The most active family of catalysts consisted of La 2O 3 on γ-Al 2O 3 prepared with lanthanum acetate and calcined at 750°C for 10 h. A maximum in rate (mol/s/g) and specific activity (mol/s/m 2) occurred between the addition of one and two theoretical monolayers of La 2O 3 on the γ-Al 2O 3 surface. The best catalyst, 40% La 2O 3/γ-Al 2O 3, had a turnover frequency at 700°C of 0.05 s −1, based on NO chemisorption at 25°C, which was 15 times higher than that for Co/ZSM-5. These La 2O 3/Al 2O 3 catalysts exhibited stable activity under high conversion conditions as well as high CH 4 selectivity (CH 4 + NO vs. CH 4 + O 2). The addition of Sr to a 20% La 2O 3/γ-Al 2O 3 sample increased activity, and a maximum rate enhancement of 45% was obtained at a SrO loading of 5%. In contrast, addition of SO =4 to the latter Sr-promoted La 2O 3/Al 2O 3 catalyst decreased activity although sulfate increased the activity of Sr-promoted La 2O 3. Dispersing La 2O 3 on SiO 2 produced catalysts with extremely low specific activities, and rates were even lower than with pure La 2O 3. This is presumably due to water sensitivity and silicate formation. The La 2O 3/Al 2O 3 catalysts are anticipated to show sufficient hydrothermal stability to allow their use in certain high-temperature applications. 相似文献
10.
Dense membranes of mixed-conducting perovskite-type oxides La 0.6Sr 0.4,CO 0.8Fe 0.2O 3 and La 0.8Ba 0.2Co 0.8Fe 0.2O 3 were used for methane coupling by application of pressure-driven O 2 permeation. High operating temperatures, typically above 800°C, were needed to obtain reasonable oxygen fluxes. Conversions were small (1–3%). Both compositions showed comparable C 2 selectivities at low methane partial pressures. At higher pressures the selectivity to C 2 hydrocarbons for La 0.6Sr 0.4CO 0.8Fe 0.2O 3 increased to 67%, whereas La 0.8Ba 0.2CO 0.8Fe 0.2O 3 showed small C 2 selectivities. Strong surface segregation of Sr and Ba was shown by SEM for both compositions. 相似文献
11.
The role of La 2O 3 loading in Pd/Al 2O 3-La 2O 3 prepared by sol–gel on the catalytic properties in the NO reduction with H 2 was studied. The catalysts were characterized by N 2 physisorption, temperature-programmed reduction, differential thermal analysis, temperature-programmed oxidation and temperature-programmed desorption of NO. The physicochemical properties of Pd catalysts as well as the catalytic activity and selectivity are modified by La2O3 inclusion. The selectivity depends on the NO/H2 molar ratio (GHSV = 72,000 h−1) and the extent of interaction between Pd and La2O3. At NO/H2 = 0.5, the catalysts show high N2 selectivity (60–75%) at temperatures lower than 250 °C. For NO/H2 = 1, the N2 selectivity is almost 100% mainly for high temperatures, and even in the presence of 10% H2O vapor. The high N2 selectivity indicates a high capability of the catalysts to dissociate NO upon adsorption. This property is attributed to the creation of new adsorption sites through the formation of a surface PdOx phase interacting with La2O3. The formation of this phase is favored by the spreading of PdO promoted by La2O3. DTA shows that the phase transformation takes place at temperatures of 280–350 °C, while TPO indicates that this phase transformation is related to the oxidation process of PdO: in the case of Pd/Al2O3 the O2 uptake is consistent with the oxidation of PdO to PdO2, and when La2O3 is present the O2 uptake exceeds that amount (1.5 times). La2O3 in Pd catalysts promotes also the oxidation of Pd and dissociative adsorption of NO mainly at low temperatures (<250 °C) favoring the formation of N2. 相似文献
12.
A series of La(Co, Mn, Fe) 1−x(Cu, Pd) xO 3 perovskites having high specific surface areas and nanosized crystal domains was prepared by reactive grinding. The solids were characterized by N 2 adsorption, X-ray diffraction (XRD), scanning electron microscopy (SEM), temperature programmed desorption (TPD) of O 2, NO + O 2, C 3H 6, in the absence or presence of 5% H 2O, Fourier transform infrared (FTIR) spectroscopy, as well as activity tests towards NO reduction by propene under the conditions of 3000 ppm NO, 3000 ppm C 3H 6, 1% O 2, 0 or 10% H 2O, and 50,000 h −1 space velocity. The objective was to investigate the influence of H 2O addition on catalytic behavior. A good performance (100% NO conversion, 77% N 2 yield, and 90% C 3H 6 conversion) was achieved at 600 °C over LaFe 0.8Cu 0.2O 3 under a dry feed stream. With the exposure of LaFe 0.8Cu 0.2O 3 to a humid atmosphere containing 10% water vapor, the catalytic activity was slightly decreased yielding 91% NO conversion, 51% N 2 yield, and 86% C 3H 6 conversion. A competitive adsorption between H 2O vapor with O 2 and NO molecules at anion vacancies over LaFe 0.8Cu 0.2O 3 was found by means of TPD studies here. A deactivation mechanism was therefore proposed involving the occupation of available active sites by water vapor, resulting in an inhibition of catalytic activity in C 3H 6 + NO + O 2 reaction. This H 2O deactivation was also verified to be strictly reversible by removing steam from the feed. 相似文献
13.
CH 4/CO 2 reforming over La 2NiO 4 and 10%NiO/CeO 2–La 2O 3 catalysts under the condition of supersonic jet expansion was studied via direct monitoring of the reactants and products using the sensitive technique of cavity ring-down spectroscopy. Vibration–rotational absorption lines of CH 4, H 2O, CO 2 and CO molecules were recorded in the near infrared spectral region. Our results indicated that La 2NiO 4 is superior to 10%NiO/CeO 2–La 2O 3 in performance. In addition, we observed enhanced reverse-water-gas-shift reaction at augmented reaction temperature. The formation of reaction intermediates was also investigated by means of time-of-flight mass spectrometry and there was the detection of CH x+, OH + and H + species. 相似文献
14.
Co 3O 4/CeO 2 composite oxides with different cobalt loading (5, 15, 30, 50, 70 wt.% as Co 3O 4) were prepared by co-precipitation method and investigated for the oxidation of methane under stoichiometric conditions. Pure oxides, Co 3O 4 and CeO 2 were used as reference. Characterization studies by X-ray diffraction (XRD), BET, temperature programmed reduction/oxidation (TPR/TPO) and X-ray photoelectron spectroscopy (XPS) were carried out. An improvement of the catalytic activity and thermal stability of the composite oxides was observed with respect to pure Co3O4 in correspondence of Co3O4–CeO2 containing 30% by weight of Co3O4. The combined effect of cobalt oxide and ceria, at this composition, strongly influences the morphological and redox properties of the composite oxides, by dispersing the Co3O4 phase and promoting the efficiency of the Co3+–Co2+ redox couple. The presence in the sample Co3O4(30 wt.%)–CeO2 of a high relative amount of Ce3+/(Ce4+ + Ce3+) as detected by XPS confirms the enhanced oxygen mobility. The catalysts stability under reaction conditions was investigated by XRD and XPS analysis of the used samples, paying particular attention to the Co3O4 phase decomposition. Methane oxidation tests were performed over fresh (as prepared) and thermal aged samples (after ageing at 750 °C for 7 h, in furnace). The resistance to water vapour poisoning was evaluated for pure Co3O4 and Co3O4(30 wt.%)–CeO2, performing the tests in the presence of 5 vol.% H2O. A methane oxidation test upon hydrothermal ageing (flowing at 600 °C for 16 h a mixture 5 vol.% H2O + 5 vol.%O2 in He) of the Co3O4(30 wt.%)–CeO2 sample was also performed. All the results confirm the superiority of this composite oxide. 相似文献
15.
Catalytic methane combustion and CO oxidation were investigated over AFeO 3 (A=La, Nd, Sm) and LaFe 1−xMg xO 3 ( x=0.1, 0.2, 0.3, 0.4, 0.5) perovskites prepared by citrate method and calcined at 1073 K. The catalysts were characterized by X-ray diffraction (XRD). Redox properties and the content of Fe 4+ were derived from temperature programmed reduction (TPR). Specific surface areas (SA) of perovskites were in 2.3–9.7 m 2 g −1 range. XRD analysis showed that LaFeO 3, NdFeO 3, SmFeO 3 and LaFe 1−xMg xO 3 ( x·0.3) are single phase perovskite-type oxides. Traces of La 2O 3, in addition to the perovskite phase, were detected in the LaFe 1−xMg xO 3 catalysts with x=0.4 and 0.5. TPR gave evidence of the presence in AFeO 3 of a very small fraction of Fe 4+ which reduces to Fe 3+. The fraction of Fe 4+ in the LaFe 1−xMg xO 3 samples increased with increasing magnesium content up to x=0.2, then it remained nearly constant. Catalytic activity tests showed that all samples gave methane and CO complete conversion with 100% selectivity to CO 2 below 973 and 773 K, respectively. For the AFeO 3 materials the order of activity towards methane combustion is La>Nd>Sm, whereas the activity, per unit SA, of the LaFe 1−xMg xO 3 catalysts decreases with the amount of Mg at least for the catalysts showing a single perovskite phase ( x=0.3). Concerning the CO oxidation, the order of activity for the AFeO 3 materials is Nd>La>Sm, while the activity (per unit SA) of the LaFe 1−xMg xO 3 catalysts decreases at high magnesium content. 相似文献
16.
One series of LaCo 1−xCu xO 3 perovskites with high specific surface area was prepared by the new method designated as reactive grinding. These solids were characterized by N 2 adsorption, X-ray diffraction (XRD), scanning electron microscopy (SEM), H 2-temperature programmed reduction (TPR), O 2-temperature programmed desorption (TPD), NO + O 2-TPD, C 3H 6-TPD, NO + O 2-temperature programmed surface reaction (TPSR) under C 3H 6/He flow as well as catalytic reduction of NO activity tests. The catalytic performance of unsubstituted sample is poor with a maximum conversion to N 2 of 19% at 500 °C at a space velocity of 55,000 h −1 (3000 ppm NO, 3000 ppm C 3H 6, 1% O 2 in helium) but it is improved by incorporation of Cu into the lattice. A maximal N 2 yield of 46% was observed over LaCo 0.8Cu 0.2O 3 under the same conditions. Not only the abundance of -oxygen but also the mobility of β-oxygen of lanthanum cobaltite was remarkably enhanced by Cu substitution according to O 2-TPD and H 2-TPR studies. The better performance of Cu-substituted samples is likely to correspond to the essential nature of Cu and facility to form nitrate species in NO transformation conditions. In the absence of O 2, the reduction of NO by C 3H 6 was performed over LaCo 0.8Cu 0.2O 3, leading to a maximal conversion to N 2 of 73% accompanied with the appearance of some organo nitrogen compounds (identified as mainly C 3H 7NO 2). Subsequently, a mechanism involving the formation of an organic nitro intermediate, which further converts into N 2, CO 2 and H 2O via isocyanate, was proposed. Gaseous oxygen acts rather as an inhibitor in the reaction of NO and C 3H 6 over highly oxidative LaCo 0.8Cu 0.2O 3 due to the heavily unselective combustion of C 3H 6 by O 2. 相似文献
17.
A new catalyst composed of nickel oxide and cerium oxide was studied with respect to its activity for NO reduction by CO under stoichiometric conditions in the absence as well as the presence of oxygen. Activity measurements of the NO/CO reaction were also conducted over NiO/γ-Al 2O 3, NiO/TiO 2, and NiO/CeO 2 catalysts for comparison purposes. The results showed that the conversion of NO and CO are dependent on the nature of supports, and the catalysts decreased in activity in the order of NiO/CeO 2 > NiO/γ-Al 2O 3 > NiO/TiO 2. Three kinds of CeO 2 were prepared and used as support for NiO. They are the CeO 2 prepared by (i) homogeneous precipitation (HP), (ii) precipitation (PC), and (iii) direct decomposition (DP) method. We found that the NiO/CeO 2(HP) catalyst was the most active, and complete conversion of NO and CO occurred at 210 °C at a space velocity of 120,000 h −1. Based on the results of surface analysis, a reaction model for NO/CO interaction over NiO/CeO 2 has been proposed: (i) CO reduces surface oxygen to create vacant sites; (ii) on the vacant sites, NO dissociates to produce N 2; and (iii) the oxygen originated from NO dissociation is removed by CO. 相似文献
18.
A comparative analysis of perovskite structured cathode materials, La 0.65Sr 0.35MnO 3 (LSM), La 0.8Sr 0.2CoO 3 (LSC), La 0.6Sr 0.4FeO 3 (LSF) and La 0.6Sr 0.4Co 0.2Fe 0.8O 3 (LSCF), was performed for a ceramic-carbonate nanocomposite fuel cell using composite electrolyte consisting of Gd 0.1Ce 0.9O 1.95 (GDC) and a eutectic mixture of Na 2CO 3 and Li 2CO 3. The compatibility of these nanocomposite electrode powder materials was investigated under air, CO 2 and air/CO 2 atmospheres at 550 °C. Microscopy measurements together with energy dispersive X-ray spectroscopy (EDS) elementary analysis revealed few spots with higher counts of manganese relative to lanthanum and strontium under pure CO 2 atmosphere. Furthermore, electrochemical impedance (EIS) analysis showed that LSC had the lowest resistance to oxygen reduction reaction (ORR) (14.12 Ω·cm 2) followed by LSF (15.23 Ω·cm 2), LSCF (19.38 Ω·cm 2) and LSM (>300 Ω·cm 2). In addition, low frequency EIS measurements (down to 50 µHz) revealed two additional semi-circles at frequencies around 1 Hz. These semicircles can yield additional information about electrochemical reactions in the device. Finally, a fuel cell was fabricated using GDC/NLC nanocomposite electrolyte and its composite with NiO and LSCF as anode and cathode, respectively. The cell produced an excellent power density of 1.06 W/cm 2 at 550 °C under fuel cell conditions. 相似文献
19.
The effect of oxygen concentration on the pulse and steady-state selective catalytic reduction (SCR) of NO with C 3H 6 over CuO/γ-Al 2O 3 has been studied by infrared spectroscopy (IR) coupled with mass spectroscopy studies. IR studies revealed that the pulse SCR occurred via (i) the oxidation of Cu 0/Cu + to Cu 2+ by NO and O 2, (ii) the co-adsorption of NO/NO 2/O 2 to produce Cu 2+(NO 3−) 2, and (iii) the reaction of Cu 2+(NO 3−) 2 with C 3H 6 to produce N 2, CO 2, and H 2O. Increasing the O 2/NO ratio from 25.0 to 83.4 promotes the formation of NO 2 from gas phase oxidation of NO, resulting in a reactant mixture of NO/NO 2/O 2. This reactant mixture allows the formation of Cu 2+(NO 3−) 2 and its reaction with the C 3H 6 to occur at a higher rate with a higher selectivity toward N 2 than the low O 2/NO flow. Both the high and low O 2/NO steady-state SCR reactions follow the same pathway, proceeding via adsorbed C 3H 7---NO 2, C 3H 7---ONO, CH 3COO −, Cu 0---CN, and Cu +---NCO intermediates toward N 2, CO 2, and H 2O products. High O 2 concentration in the high O 2/NO SCR accelerates both the formation and destruction of adsorbates, resulting in their intensities similar to the low O 2/NO SCR at 523–698 K. High O 2 concentration in the reactant mixture resulted in a higher rate of destruction of the intermediates than low O 2 concentration at temperatures above 723 K. 相似文献
20.
Initial tests have been carried out with the fuel cell arrangement La 0.6Sr 0.4Co 0.2Fe 0.8O 3Ce 0.9Gd 0.1O 1.95Ni/YSZ, incorporating dense film (5–10 μm) Ce 0.9Gd 0.1O 1.95 electrolyte tape cast onto the supporting anode, to investigate the feasibility of intermediate temperature operation (500–700°C). A good open circuit voltage of approx. 0.8 V was obtained at 550°C using moist hydrogen as the fuel. Slightly lower open circuit voltages were found at higher temperatures, which may have been caused by minor gas leakage and the electronic conductivity of the electrolyte. Power outputs in excess of 100 mW/cm 2 were obtained at 650°C, and the cell resistance was 0.8Ω cm 2 at this temperature. This resistance, and the greater resistance at lower temperature, was predominantly due to the cathode according to AC impedance measurements. Experiments were also carried out at 600°C using direct methanol fuels at the anode; the maximum power output was approximately half of that obtained with hydrogen. 相似文献
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