首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 15 毫秒
1.
The transient behaviour caused by the change of the component concentration for CO oxidation on the perovskite‐type catalyst La0.4Sr0.6Co0.4Mn0.6O3 was investigated. Results showed that CO was not adsorbed on the catalyst surface and CO oxidation was carried out between the surface oxygen species and gas phase CO. On the other hand, CO2 can be adsorbed on the catalyst surface but its adsorption site was different from the forming site.  相似文献   

2.
Small Co clusters (d<10 nm) supported over mixed La–Co–Fe perovskites were successfully synthesized. These catalysts were active for Fischer–Tropsch (FT). Depending on the Co to Fe ratios the mixed perovskite exhibited two different forms: the rhombohedral phase of LaCoO3 is maintained for the mixed perovskite when x>0.5, the orthorhombic phase of LaFeO3 is found for x<0.5. Interestingly only one of these structures is active for the FT reaction: the orthorhombic structure. This is most likely due to the capacity of this material to maintain its structure even with a high number of cation vacancies. These cations (mostly Co) were on purpose extracted and reduced. Magnetic measurements clearly showed their metallic nature. Rhombohedral Co–Fe mixed perovskites (x≥0.5) cannot be used as precursors for Fischer–Tropsch catalysts: their partial reduction only consists in a complete reduction of Co3+ into Co2+.

The partial reduction of orthorhombic perovskites (x<0.5) leads to active Fischer–Tropsch (FT) catalysts by formation of a metal phase well dispersed on a cation-deficient perovskite. The FT activity is related to the stability of the precursor perovskite. When initially calcined at 600 °C, a maximum of 8.6 wt.% of Co0 can be extracted from LaCo0.40Fe0.60O3 (compared to only 2 wt.% after calcination at 750 °C). The catalyst is then composed of Co0 particles of 10 nm on a stable deficient perovskite LaCo0.053+Fe0.603+O2.40. Catalytic tests showed that up to 70% in the molar selectivity for hydrocarbons was obtained at 250 °C, 40% of which was composed of the C2–C4 fraction.  相似文献   


3.
以高锰酸钾和葡萄糖为原料,通过水热反应制备了四氧化三锰纳米晶颗粒,探讨了过渡金属离子掺杂的影响,并考察制备的产物作为催化剂在催化一氧化碳氧化反应中的性能。采用X射线衍射(XRD)、扫描电镜 (SEM)、透射电镜(TEM)、X射线光电子能谱(XPS)、氢气程序升温还原(H2-TPR)等手段对产物进行结构表征。结果表明,过渡金属离子掺杂可消除产物中的MnOOH杂相。制备的产物具有八面体形貌,尺寸随掺杂离子的变化而变化。掺杂还可以提高四氧化三锰纳米晶催化一氧化碳氧化反应的活性,呈现掺杂效应。  相似文献   

4.
Two nanostructured bulk LaCoO3 powders were prepared by co-precipitation and with the citrate gel method and compared with the two nanocomposites obtained depositing, by wet impregnation, cobalt oxide on the La2O3 surface. All the prepared samples were characterized by means of X-ray photoelectron (XP) and diffuse reflectance infrared Fourier transform (DRIFT) spectroscopic techniques, X-ray diffraction (XRD), scanning electron microscopy (SEM) and thermal analysis.

XRD results suggest that only the citrate gel method allows to obtain a single phase lanthanum cobaltite powder having a rhombohedral perovskite structure. Moreover, SEM images confirm the wide scale homogeneity. In contrast, a lanthanum hydroxide phase (hexagonal) is also evident in the sample obtained by co-precipitation method. In the nanocomposite richer in cobalt, besides the rhombohedral perovskite, the hexagonal lanthanum oxide and hydroxide phases are also detectable. Perovskite phase does not form when the amount of deposited cobalt oxide is too low. Both in the nanostructured sample prepared by citrate gel method and nanocomposite with [Co/La]nominal = 1.0 XPS, DRIFT and TGA outcomes suggest a lower presence of hydroxyl groups and carbonates species.

The reactivity of the powders with respect to carbon monoxide was studied (at atmospheric pressure, between RT and 573 K) by means of the diffuse reflectance infrared Fourier transform spectroscopy. A significant signal around 2058 cm−1 testifies about the interaction of CO with the Lewis acidic sites distributed on the surface of all the samples. The two nanostructured bulk LaCoO3 show a high reactivity toward CO oxidation since 423 K. A similar oxidation capability is observed also for the nanocomposite richer in cobalt. In contrast, a rather low reactivity is displayed from the nanocomposite with lower Co/La nominal atomic ratio and La2O3.  相似文献   


5.
以合成中温固体氧化物燃料电池阴极La0.7Sr0.3Fe0.8Co0.2O3(LSFC)粉体为研究对象,探讨了PVA改进的溶胶凝胶法合成粉体的影响因素,获得最优实验条件。当pH值=7,柠檬酸与金属离子摩尔比为1.6∶1;PVA与硝酸盐质量比为1∶4时,能够形成形态良好且透明澄清的溶胶,再经12 h的陈化形成凝胶,然后在155℃烘箱中使凝胶膨化制得LSFC前驱体。LSFC前躯体在900℃煅烧2 h后形成晶体结构稳定、粒径分布均匀、具有单一钙钛矿结构的粉体。  相似文献   

6.
香兰素与丙二酸于乙酸正丁酯中,在KF/K2CO3/γ-Al2O3催化作用下,经Knoevenagel制得反式阿魏酸。收率为65.4%,纯度达到99.7%。  相似文献   

7.
Nano-oxide hollow structures have a wide range of applications in catalysis, but the preparation of multi-shelled composite oxide hollow structures still presents a major challenge. Herein, well-dispersed multi-shelled MnO2–Co3O4 hollow spheres have been successfully prepared via a facile “Kirkendall effect” method employing carbon spheres as sacrifice templates. The shell of the hollow spheres was constructed by interconnected Co3O4 nanosheets and catkin-like MnO2 nanorods. The interdiffusion of Carbon chain and MnO4? during synthesis could be the possible formation mechanism for the special morphology. Benefiting from the hierarchical porous structure, high surface area and strong synergistic effect between Co3O4 and MnO2 was obtained, the as-prepared Co–Mn composite hollow spheres showed reliably high activity and recycle stability for CO oxidation, achieving the complete CO conversion at 137 °C without significant decrease in activity after five cycles and 10h constant-temperature reaction. We believe that this work will provide a new method for the preparation of multi-shell composite hollow spheres.  相似文献   

8.
丁方园 《山西化工》2011,31(3):39-42
运用广义梯度密度泛函理论方法(density functional theory,DFT),结合周期性平板模型,研究了CO2在La2O3(011)表面的吸附和活化,计算了CO2吸附的吸附能和Mulliken电荷数.结果表明,CO2在La2O3(011)表面吸附形成6种平衡构型,分别为CO2-η1、CO2-η2、CO2-...  相似文献   

9.
王柯晴  徐劼  沈芷璇  陈家斌  吴玮 《化工学报》2020,71(3):1326-1334
在催化活化过一硫酸盐(PMS)降解水中污染物的反应中,通过添加钴基钙钛矿提高反应效率。利用溶胶凝胶法制备了LaCoO3钙钛矿,通过实验评估LaCoO3/PMS体系对非甾体抗炎药萘普生(NAP)的降解效果。分析了LaCoO3投加量、PMS投加量、反应初始pH、Cl-浓度和腐殖酸(HA)对NAP去除率的影响以及该体系的矿化能力。结果表明NAP降解的反应速率随LaCoO3和PMS投加量增加而增大;反应初始pH在5.0时NAP降解效果最好;溶液中存在Cl-对降解有促进效果,且Cl-浓度越大促进效果越明显;腐殖酸(HA)对反应有一定程度的抑制效果;LaCoO3在重复利用5次时仍有较好的稳定性。此外,自由基淬灭实验结果表明在LaCoO3/PMS体系中SO4·-为主要活性物质。  相似文献   

10.
Barium, lanthanum, and praseodymium perovskites were prepared by malic acid complexation. Surface areas of the La and Pr perovskites were between 17.1 and 21.6 m2 g−1. The moderate low surface areas (5.7 m2 g−1) observed for corresponding barium perovskites were due to the high calcination temperatures. The calcination temperature also affected the shapes and sizes of the perovskite particles. According to SEM images the nanoparticles of the La and Pr perovskites were spherical, whereas those of barium perovskites were flakes. The conversion of methane increased in the order of A-site metal Ba < Pr < La. The CH4 conversion after SO2 treatment correlated with size of the perovskite particles: the smaller the particles the better the activity. The highest methane conversion after SO2 treatment was achieved with lanthanum perovskite with B-site metal combination Mn0.4Fe0.6.  相似文献   

11.
(La,Sr)(Co,Fe)O3 (LSCF) perovskites are well known promising materials for cathodes of solid oxide fuel cells. In order to reduce cathode operational temperature, doping on B‐sublattice with different metals was suggested. Indeed, as it was shown recently experimentally, doping with low Pd content increases oxygen vacancy concentration which is one of factors controlling oxygen transport in fuel cells. In this Communication, we modeled this material using first principles DFT calculations combined with supercell model. The charge density redistribution, density of states, and local lattice distortion around palladium ions are analyzed and reduction of the vacancy formation energy confirmed.  相似文献   

12.
本文介绍了羟基天冬氨酸合成的,以D-酒石酸二乙酯为原料,与氯化亚砜反应成亚磺酸类化合物,再与叠氮化钠发生开环反应后,催化加氢还原后得到羟基天冬氨酸二乙酯,经皂化反应后得到目标产物,四步反应的总收率为42.04%。  相似文献   

13.
以Bi(NO3)3·5H2O、Co(CH3COO)2·4H2O为原料,采用化学沉淀-水热法制备了Co3O4-Bi2O2CO3异质结构复合半导体光催化剂,并通过X射线衍射仪(XRD)、扫描电镜(SEM)、X射线光电子能谱(XPS)、紫外可见漫反射光谱(DRS)、荧光光谱(PL)等手段对所合成的复合型催化剂进行了理化性能表征。研究结果表明:引入Co3O4没有改变Bi2O2CO3物相结构,但促进了Bi2O2CO3 对可见光的吸收能力,提高了Bi2O2CO3表面吸附氧物种的数量,抑制了光生载流子复合。复合光催化剂对罗丹明B(RhB)的光催化脱色实验显示引入Co3O4能够明显提高Bi2O2CO3催化剂的光催化脱色能力。尤其是Co3O4引入量为0.6%的Co3O4-Bi2O2CO3样品对罗丹明B染料的光催化脱色率可达到97%(模拟日光照射30min)。本文为复合型光催化剂制备提供了简单易行的技术路线,制备的新型半导体复合光催化剂Co3O4-Bi2O2CO3在环境净化方面表现出了较好的应用前景。  相似文献   

14.
合成了磁性固体酸ZrO2/Fe3O4,运用X-射线衍射(XRD),差热(DTA),对其进行了表征,考察了合成条件对催化剂活性的影响。  相似文献   

15.
Electrochemical performance and degradation was analysed by conductivity measurements as well as thermogravimetric analysis (TGA) under different atmospheres. CO2 was identified as a critical parameter in terms of carbonate formation from Ba0.5Sr0.5Co0.8Fe0.2O3–δ and causes a strong increase in the material resistivity, whereas La0.6Sr0.4Co0.2Fe0.8O3–δ is unaffected. The oxygen exchange kinetic of both compositions is affected by CO2 containing atmospheres.  相似文献   

16.
A green synthetic method using mixted solvents of di-methyl formamide (DMF) and acids instead of single DMF to synthesize metalloporphyrins (TRPPMCl) from TRPPH2 and MCl2 metallization was proposed in this paper. A series of TRPPMCl (M = Fe, Mn, Co) were synthesized through this innovative synthetic method, and these complexes were characterized with various spectroscopic techniques, including IR and UV-Vis spectroscopy. The results showed that the metallization time was markedly reduced from about 10 h to 0.5 h in contrast with the conventional synthetic methods.  相似文献   

17.
不同水热条件下氧化镧的制备和表征   总被引:1,自引:0,他引:1  
以硝酸镧溶液为原料,以聚乙二醇800为分散剂,用六次甲基四胺作沉淀剂,经水热反应制取前驱体,再经焙烧制得纳米氧化镧。考察了不同水热条件,如水热温度,反应时间,前驱物浓度和冷却方式对制备产品形貌的影响,采用XRD和TEM对粉体进行了表征。结果表明,氧化镧颗粒随着水热温度的提高,反应时间的增长以及前驱物浓度的提高而逐渐长大,团聚现象逐渐加剧;自然冷却方式较之骤冷的方式更加有利于形成小颗粒的氧化镧产品。  相似文献   

18.
A green synthetic method using mixted solvents of di-methyl formamide(DMF) and acids instead of single DMF to synthesize metalloporphyrins(TRPPMCl) from TRPPH2 and MCl2 metallization was proposed in this paper. A series of TRPPMCl (M= Fe, Mn, Co) were synthesized through this innovative synthetic method, and these complexes were characterized with various spectroscopic techniques, including IR and UV-Vis spectroscopy. The results showed that the metallization time was markedly reduced from about 10 h to 0.5 h in contrast with the conventional synthetic methods.  相似文献   

19.
以2-对硝基苄氧羰基甲氧亚胺基-3-氧代丁酸、磺酰氯为起始原料,在一定条件下经过反应、处理,得到(顺式或反式)即(Z或E)-4-氯-2-对硝基苄氧羰基甲氧亚胺-3-氧代丁酸。通过红外、核磁共振对其结构进行了表征。较佳工艺条件:原料摩尔比n(2-对硝基苄氧羰基甲氧亚胺基-3-氧代丁酸)∶n(磺酰氯)=1∶1.4,在50~55℃反应5~6 h,反应完调节体系pH值为6.5±0.1,顺式、反式异构体产品分离效果达到99%以上,收率分别是24%和48%,纯度均为98%。  相似文献   

20.
Novel Rh–La(Mn,Co)O3 structured catalysts were developed for the partial oxidation of methane to syngas intended as a preliminary conversion step in combustion systems such as power turbines and utility burners employing a fuel-rich fuel-lean approach to reduce NOx formation. Active components were impregnated on La–γ-Al2O3 washcoated honeycomb monoliths and the catalysts were characterised by BET, SEM/EDS, H2-TPR, and in situ FT-IR under reaction conditions. Catalytic partial oxidation of methane was tested under both pseudo-isothermal and pseudo-adiabatic conditions showing that the process can be conducted with high yield and selectivity: improved and stable performances were found especially in the case of Rh–LaMnO3 catalyst, due to the synergism between active sites and to the stabilization of the noble metal.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号