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1.
Perovskite-type La 0.8Sr 0.2CoO 3 mixed oxides were prepared by d, l-alanine solution combustion synthesis and used successfully in CH 4 combustion as catalysts. These samples were characterized by means of XRD, FTIR, BET, and H 2-TPR methods. The effects of stoichiometric ratio (φ) of organic fuel to oxidizer on the structure and catalytic activities
of the catalysts were studied. The results indicate that all La 0.8Sr 0.2CoO 3 mixed oxides with different φ have perovskite structures. Their structures and catalytic activities vary along with the change of φ. The catalytic activity
of La 0.8Sr 0.2CoO 3 mixed oxide with φ = 1.52 is the best among all the samples, whose T
50 and T
100 (the temperatures of methane conversions reaching 50 and 100%, respectively) are respectively 470 °C and 550 °C, which can
be explained in terms of the smaller of average crystal size, higher specific surface area, bigger lattice distortion, lower
activation energy, and higher mobility of chemically adsorbed oxygen on the surface and vacancy of the catalysts. 相似文献
2.
采用甘氨酸-硝酸盐溶液燃烧法制备了钙钛矿型氧化物催化剂La 0.8Sr 0.2Fe 1-xSc xO 3-δ (LSFS, x=0, 0.3,0.4, 0.5, 0.6, 0.8, 1), 利用X射线衍射(XRD)、H 2程序升温还原(H 2-TPR)、扫描电子显微镜(SEM)和比表面积测试等手段对催化剂进行了系统表征, 并在常压微型固定床反应器上考察了催化剂对甲烷燃烧的催化性能. 结果表明, 经空气气氛下900 °C煅烧5 h制备的LSFS均具有单一的钙钛矿结构, 在La 0.8Sr 0.2FeO 3-δ (LSF)中掺杂Sc有助于改善催化剂的抗烧结性能, 提高催化剂的比表面积. 当LSF 中的Sc 掺杂量为0.4-0.6 时, 所形成的LSFS表现出良好的甲烷催化燃烧活性, 其中Sc 掺杂量为0.5 时, 其起燃温度(T 10)和完全转化温度(T 90)分别为406和563 °C, 与La 0.8Sr 0.2FeO 3-δ和La 0.8Sr 0.2ScO 3-δ相比, T 10分别降低了14和87 °C; T 90分别降低了59和95 °C. 相似文献
3.
Porous perovskite-type complex oxides LaCoO 3 and La 0·95Sr 0·05Ni 0·05Co 0·95O 3 were produced by combustion method. The properties of these porous materials such as crystal structures, particle sizes,
surface patterns, pore size, surface area and pore volume were characterized by X-ray diffraction( XRD), scanning electron
microscopy(SEM) and BET measurements. The results indicated that all porous materials are of the perovskite-type complex oxides.
Doping Sr 2+ ions on site A and doping Ni 2+ ions on site B entered the crystal lattices of LaCoO 3 in the place of La 3+ and Co 3+, respectively, and the maximum peak of XRD patterns of doping sample was weaken and broaden. Morphological microscopy demonstrated
agglomerates involved mostly thin smooth flakes and layers perforated by a large number of pores and its lamella decreased
with the introduction of Sr 2+ and Ni 2+. Hysteresis loop in the N 2 adsorption-desorption isotherm of samples indicated its porous structures and the doping effect on its pore size, surface
area and pore volume were improved. The porous catalysts have been tested for methane catalytic combustion and the results
showed that these catalysts possessed high catalytic activity. 相似文献
4.
A series of catalysts La 0.95Ce 0.05CoO 3, La 0.95Ce 0.05Co 0.95Pt 0.05O 3 and Pt/La 0.95Ce 0.05CoO 3 were prepared by combustion method and impregnation method, respectively. The purpose of the present work was to study the
effect of platinum, with the same loading, on the platinum-substituted perovskite and perovskite-supported platinum catalyst.
The catalysts structure were characterized by X-ray diffraction (XRD), BET measurements, transmission electron micrographs
(TEM) and the methane oxidation activity of the catalysts were investigated in detail. It was found that the catalytic activity
of La 0.95Ce 0.05Co 0.95Pt 0.05O 3 was superior to that of La 0.95Ce 0.05CoO 3 and the activity performance of Pt/La 0.95Ce 0.05CoO 3 was higher than that of La 0.95Ce 0.05Co 0.95Pt 0.05O 3 for methane combustion. 相似文献
5.
Ultra-fine particles of La 0.5RE 0.1Sr 0.4MnO 3 (RE: Y, Dy, Sm or Ce) with perovskite structure were prepared by the co-precipitation method, resulting in high surface area and good thermal stability catalysts (S BET reached 45 and 16.5 m 2/g, upon calcination at 700 and 1000 oC, respectively). The thermal stability of these ultra-fine particles was effectively improved with partial substitution of RE 3+ (Y 3+, Dy 3+, or Sm 3+) for La 3+ in La 0.6Sr 0.4MnO 3. The catalysts exhibited high activity for the total combustion of methane. For the catalysts calcined at 1000 oC, La 0.5RE 0.1Sr 0.4MnO 3 (RE: Y or Dy) were much more active and showed much higher specific surface area than La 0.6Sr 0.4MnO 3. 相似文献
6.
Comparison of LaFeO3, La0.8Sr0.2FeO3, and La0.8Sr0.2Fe0.9CO0.1O3 perovskite oxides as oxygen carrier for partial oxidation of methane in the absence of gaseous oxygen was investigated by continuous flow reaction and sequential redox reaction, Methane was oxidized to syngas with high selectivity by oxygen species of perovskite oxides in the absence of gaseous oxygen. The sequential redox reaction revealed that the structural stability and continuous oxygen supply in redox reaction decreased over La0.8Sr0.2Fe0.9Co0. 1O3 oxide, while LaFeO3 and La0.8Sr0.2FeO3 exhibited excellent structural stability and continuous oxygen supply. 相似文献
7.
La1-xAxCoO3-δ (A = Sr, Ba) nanoparticles used as an inert anode in molten salts were characterized using phonon vibrations, and their compositions and morphologies were investigated. These nanoparticles were used for nanostructure fabrication of an inert anode to reduce oxide ion transportation. The singularity structure changes with increasing Sr ion content in La1-xSrxCoO3-δ nanoparticles showed a transient of spin state change from a low-spin state to intermediate- and/or high-spin states. The valencies of Co ion in La1-xSrxCoO3-δ were 3.2 and 3.3 for La0.8Sr0.2CoO3-δ and La0.6Sr0.4CoO3-δ, respectively, suggesting that oxygen defects were introduced by Sr ion doping in La1-xSrxCoO3-δ nanoparticles. In contrast, the valencies of Co ion in La1-xBaxCoO3-δ were 3.1 and 3.0 for La0.5Ba0.5CoO3-δ and La0.4Ba0.6CoO3-δ, respectively, suggesting that oxygen defects were introduced slightly by Ba ion doping in La1-xBaxCoO3-δ nanoparticles. The isotropic phonon vibrations of La1-xAxCoO3-δ nanoparticles were estimated using high-temperature synchrotron radiation X-ray diffraction measurements. Crystal anisotropy measurements of phonon vibrations indicated that the oxide ions diffused preferentially along the (a, b) plane in the La1-xSrxCoO3-δ crystal lattice and toward the c-axis direction in the La1-xBaxCoO3-δ crystal lattice. These results suggest that the oxide ion transportation was curtailed using layered nanoparticles to fabricate an inert anode. 相似文献
8.
The development of non-precious metal catalysts with excellent bifunctional activities is significant for air–metal batteries. ABO 3-type perovskite oxides can improve their catalytic activity and electronic conductivity by doping transition metal elements at B sites. Here, we develop a novel Sm 0.5Sr 0.5Co 1−xNi xO 3−δ (SSCN) nanofiber-structured electrocatalyst. In 0.1 M KOH electrolyte solution, Sm 0.5Sr 0.5Co 0.8Ni 0.2O 3−δ (SSCN82) with the optimal Co: Ni molar ratio exhibits good electrocatalytic activity for OER/ORR, affording a low onset potential of 1.39 V, a slight Tafel slope of 123.8 mV dec −1, and a current density of 6.01 mA cm −2 at 1.8 V, and the ORR reaction process was four-electron reaction pathway. Combining the morphological characteristic of SSCN nanofibers with the synergistic effect of cobalt and nickel with a suitable molar ratio is beneficial to improving the catalytic activity of SSCN perovskite oxides. SSCN82 exhibits good bi-functional catalytic performance and electrochemical double-layer capacitance. 相似文献
9.
Phases formed by the reduction of compounds of the type La 0.5Sr 0.5MO 3 ( M=Fe, Co) have been characterized by means of temperature programmed reduction, X-ray powder diffraction, 57Fe Mössbauer spectroscopy and Fe K-, Co K-, Sr K-, and La L III-edge X-ray absorption spectroscopy. The results show that treatment of the material of composition La 0.5Sr 0.5FeO 3 (which contains 50% Fe 4+ and 50% Fe 3+) at 650 °C in a flowing 90% hydrogen/10% nitrogen atmosphere results in the formation of an oxygen-deficient perovskite-related phase containing only trivalent iron. Further heating in the gaseous reducing environment at 1150 °C results in the formation of the Fe 3+-containing phase SrLaFeO 4, which has a K 2NiF 4-type structure, and metallic iron. The material of composition La 0.5Sr 0.5CoO 3 is more susceptible to reduction than the compound La 0.5Sr 0.5FeO 3 since, after heating at 520 °C in the hydrogen/nitrogen mixture, all the Co 4+ and Co 3+ are reduced to metallic cobalt with the concomitant formation of strontium- and lanthanum-oxides. 相似文献
10.
The M 4+-containing K 2NiF 4-type phases La 0.8Sr 1.2Co 0.5Fe 0.5O 4 and La 0.8Sr 1.2Co 0.5Mn 0.5O 4 have been synthesized by a sol–gel procedure and characterized by X-ray powder diffraction, thermal analysis, neutron powder diffraction and Mössbauer spectroscopy. Oxide ion vacancies are created in these materials via reduction of M 4+ to M 3+ and of Co 3+ to Co 2+. The vacancies are confined to the equatorial planes of the K 2NiF 4-type structure. A partial reduction of Mn 3+ to Mn 2+ also occurs to achieve the oxygen stoichiometry in La 0.8Sr 1.2Co 0.5Mn 0.5O 3.6. La 0.8Sr 1.2Co 0.5Fe 0.5O 3.65 contains Co 2+ and Fe 3+ ions which interact antiferromagnetically and result in noncollinear magnetic order consistent with the tetragonal symmetry. Competing ferromagnetic and antiferromagnetic interactions in La 0.8Sr 1.2Co 0.5Fe 0.5O 4, La 0.8Sr 1.2Co 0.5Mn 0.5O 4 and La 0.8Sr 1.2Co 0.5Mn 0.5O 3.6 induce spin glass properties in these phases. 相似文献
11.
In this work, we studied the catalytic activity of LaMnO 3 and (La 0.8A 0.2)MnO 3 (A = Sr, K) perovskite catalysts for oxidation of NO and C 10H 22 and selective reduction of NO by C 10H 22. The catalytic performances of these perovskites were compared with that of a 2 wt% Pt/SiO 2 catalyst. The La site substitution increased the catalytic properties for NO or C 10H 22 oxidation compared with the non-substituted LaMnO 3 sample. For the most efficient perovskite catalyst, (La 0.8Sr 0.2)MnO 3, the results showed the presence of two temperature domains for NO adsorption: (1) a domain corresponding to weakly adsorbed NO, desorbing at temperatures lower than 270 ℃ and (2) a second domain corresponding to NO adsorbed on the surface as nitrate species, desorbing at temperatures higher than 330 ℃. For the Sr-substituted perovskite, the maximum NO 2 yield of 80% was observed in the intermediate temperature domain (around 285 ℃). In the reactant mixture of NO/C 10H 22/O 2/H 2O/He, (La 0.8Sr 0.2)MnO 3 perovskite showed better performance than the 2 wt% Pt/SiO 2 catalyst: NO 2 yields reaching 50% and 36% at 290 and 370 ℃, respectively. This activity improvement was found to be because of atomic scale interactions between the A and B active sites, Sr 2+ cation and Mn 4+/Mn 3+ redox couple. Thus, (La 0.8Sr 0.2)MnO 3 perovskite could be an alternative free noble metal catalyst for exhaust gas after treatment. 相似文献
12.
A series of mixed oxides Sr 4Fe 6?xCo xO 13?δ ( x=0, 1, 2, 3, or 4) were prepared by sol‐gel method and used for catalytic combustion of methane. The structural properties of oxides were characterized by XRD, TGA, and XPS. The layered intergrowth perovskite‐like oxide Sr 4Fe 5CoO 13?δ exhibits the highest catalytic activity for methane combustion under the experimental conditions. The enhanced catalytic activity of Sr 4Fe 5CoO 13?δ for methane combustion could be attributed to the increased amount of oxygen vacancy caused by the partial substitution of cobalt for iron in the Sr 4Fe 6O 13, which was confirmed by TGA and XPS. 相似文献
13.
Li-O 2 batteries (LOBs) with an extremely high theoretical energy density have been reported to be the most promising candidates for future electric storage systems. Porous catalysts can be beneficial for LOBs. Herein, 3D-ordered macroporous La 0.6Sr 0.4Co 0.2Fe 0.8O 3 perovskite oxides (3D-LSCF) are applied as cathode catalysts in LOBs. With a high Brunauer-Emmett-Teller surface area (21.8 m 2 g −1) and unique honeycomb-like macroporous structure, the 3D-LSCF catalysts possess a much higher efficiency than La 0.6Sr 0.4Co 0.2Fe 0.8O 3 (LSCF) nanoparticles. The unique 3D-ordered macropores play a significant role in the product deposition as well as oxygen and electrolyte transmission, which are crucial for the discharge-charge processes of LOBs. 相似文献
14.
Methane transformation over Ni and Cu modified Sr 2+/La 2O 3 catalysts has been studied. These species favor formation of reducible mixed oxides and change the surface reactivity of the Sr 2+/La 2O 3 system, modifying the reaction mechanism, since Sr 2+/La 2O 3 favors methane oxidative coupling but with copper methane combustion is favored and nickel favors partial oxidation. 相似文献
15.
La 0.5Sr 0.5MnO 3 nanowires and nanoparticles were synthesized by the hydrothermal and citrate methods, respectively. The samples were characterized by TEM, HRTEM, XRD, ICP and N 2 adsorption, etc. The formation mechanism of the nanowires was proposed and discussed. Further, the stabilities and catalytic activities of La 0.5Sr 0.5MnO 3 nanowires for CH 4 combustion were evaluated and compared with those of the nanoparticles. The results showed that the particle morphology had a significant effect on the properties of the catalysts. After running at a high temperature for a long duration, the nanowires showed a higher stability and a higher activity, compared with the nanoparticles. Their different stabilities were ascribed to the different surface energies (particle sizes), as well as to the different geometric packing models. 相似文献
16.
采用溶胶-凝胶法制备了一系列La 1-xSr xNi 1-yFe yO 3 ( x=0, 0.1, 0.2, 0.5; y=0~1.0)型的钙钛矿催化剂, 以活性碳为载体, PTFE乳液为粘接剂制备双功能氧电极. 对催化剂进行了XRD结构分析以及SEM分析和BET比表面积测量. 采用三电极体系测试了氧电极的稳态极化曲线和电化学交流阻抗谱并对其阴极极化和阳极极化的交流阻抗谱图进行分析. 通过等效电路的拟合研究了该系列双功能氧电极氧还原反应的工作机理. 实验表明对于LaNiO 3化合物, B位掺杂可显著提高催化剂的电催化性能; 电极氧还原反应的极化主要由电荷转移反应和Nernstian扩散过程造成. 通过各个电极对于催化分解H 2O 2的分解速率常数的测定得知, Ni离子对于催化H 2O 2分解反应的活性大于Fe离子, 继续在对于氧还原反应和氧析出反应都具有较高电催化活性的LaNi 0.8Fe 0.2O 3催化剂上进行A位掺杂Sr离子后显著提高了催化剂分解H 2O 2的催化活性, 主要是因为氧空位的增多和金属离子d电子含量的降低有利于催化分解H 2O 2的活性的提高, 但由于氧空位的增多导致催化剂电导率的降低, 所以其电催化活性降低了. 通过多圈循环伏安扫描的测试, 催化剂LaNi 0.8Fe 0.2O 3有很好的稳定性. 相似文献
17.
A system consisting of a solid oxide electrolyte of the Ce 0.9Gd 0.1O 2 − x
(CGO) composition in contact with a two-layer cathode based on a nonstoichiometric composition (La 0.8Sr 0.2) 0.95MnO 3 ± δ (LSM1) and a stoichiometric perovskite La 0.8Sr 0.2MnO 3 ± δ (LSM2) is prepared by the tape-casting process. It was shown that the best electrochemical characteristics are achieved for
a three-layer system LSM2/{CGO-LSM1}/CGO sintered at 1410°C. The use of Ce-modified perovskites La 0.8Sr 0.2MnO 3 ± δ and La 0.6Sr 0.6CoO 3 ± δ as the collector layer of two-layer electrodes allows the electrochemical characteristics at moderately high temperatures
(600–750°C) to be improved. 相似文献
18.
Thin films of La 1−xSr xCoO 3, Nd 0.5Sr 0.5CoO 3, Gd 0.5Sr 0.5CoO 3 and SrRuO 3 have been deposited on Si(100), LaAlO 3(100) and SrTiO 3(100) single crystal substrates by nebulized spray pyrolysis. The films deposited on Si are generally polycrystalline, but they are highly oriented on the oxide substrates. The cobaltate films are generally not metallic, but exhibit low resistivity specially when x=0.3 and 0.5, the latter also exhibiting ferromagnetic characteristics. Films of La 0.7Sr 0.3CoO 3 show negative magnetoresistance of 35% around 180 K. Films of SrRuO 3 are metallic on Si and LaAlO 3 substrates but show an insulator–metal transition on SrTiO 3 around 130 K, around which temperature negative magnetoresistance is observed. 相似文献
19.
It was found that the oxygen evolution reaction on La 0.5Sr 0.5CoO 3 in strong alkaline solutions has a Tafel slope of ~ 60 mV/dec and a reaction order at constant overpotential with respect to the KOH activity of 0.6–0.8. From impedance measurements differential Tafel slopes were calculated and were found to be ~ 60 mV/dec at overpontentials > 250 mV. Effective capacitances having a broad maximum at an overpotential of about 200 mV in all alkaline solutions were calculated. The effective capacitance increased with increasing KOH concentration. Furthermore, the material decomposed at the surface when exposed to strong oxygen evolution. From the results a modified Krasil'shchikov reaction path is analysed. 相似文献
20.
采用固相反应法合成了钙铝石材料 12SrO•7Al2O3, 并以此作为涂层制备了堇青石蜂窝陶瓷型 La0.8Sr0.2MnO3 整体催化剂, 在不同温度 (850~1 050 oC) 下对该催化剂进行了热处理, 并采用 N2 吸附-脱附、X 射线衍射和扫描电镜等手段对其进行了表征, 考察了其催化甲基丙烯酸甲酯燃烧反应的活性. 结果表明, 12SrO•7Al2O3 作为涂层明显改善了整体催化剂的热稳定性, 在 850 oC 下焙烧 6 h 后, 含有 12SrO•7Al2O3 涂层的整体催化剂在 260 oC 即可将甲基丙烯酸甲酯完全转化. 12SrO•7Al2O3 涂层可避免 La0.8Sr0.2MnO3 活性组分与堇青石的接触, 减轻了活性组分在催化剂表面的烧结, 有利于保持 La0.8Sr0.2MnO3 活性组分的晶体结构和分散度, 提高整体催化剂的活性和热稳定性. 相似文献
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