共查询到20条相似文献,搜索用时 15 毫秒
1.
Three types of supported cobalt catalysts (CoOx/SiO2, CoOx/TiO2 and CoOx/Al2O3) were prepared by incipient wetness impregnation with aqueous Co(NO3)2·6H2O solution. The phase composition and the interactions of cobalt with supports under different calcined temperatures were
investigated using thermogravimetry (TG), N2-adsorption at −196 °C, X-ray diffraction (XRD), temperature-programmed reduction (TPR) and diffuse reflectance spectroscopy
(DRS). Their catalytic activities towards the CO oxidation were further studied in a continuous flow micro-reactor. The results
showed that the interaction of cobalt oxide with supports was much stronger in the kinds of Al2O3 and TiO2, while no conclusive evidence of any interaction was found for SiO2. Besides the crystalline Co3O4 which was formed in three supported catalysts, both high-temperature phases CoAl2O4 and CoTiO3 spinel were also detected under XRD, DRS and TPR analysis. The degree of interaction between cobalt oxide and the support
not only affected the surface area and reduction behavior of the catalysts, the catalytic activity toward the CO oxidation
also affected simultaneously. As the CoAl2O4 and CoTiO3 spinel formed, both the surface area and catalytic activity decreased significantly. 相似文献
2.
3.
4.
Roya Dehghan Thomas W. Hansen Jakob B. Wagner Anders Holmen Erling Rytter Øyvind Borg John C. Walmsley 《Catalysis Letters》2011,141(6):754-761
Abstract
Reduction of 12wt.%Co/0.5wt.%Re/α-Al2O3 Fischer–Tropsch catalyst has been studied in-situ in an environmental transmission electron microscope. Reduction of Co3O4 to metallic cobalt was observed dynamically at 360 °C under 3.4 mbar H2. Structural and morphological changes were observed by high resolution transmission electron microscopy and scanning transmission electron microscopy imaging. The cobalt particles were mainly face centred cubic while some hexagonal close packed particles were also found. Reoxidation of the sample upon cooling to room temperature, still under flowing H2, underlines the reactivity of the nanoparticles and the importance of controlling the gas composition and specimen temperature during this type of experiment. Similar behaviour was observed for a non-promoted catalyst. Imaging and analysis of the promoted sample before and after reduction indicated a uniform distribution of the promoter. 相似文献5.
6.
Chen-Bin Wang Chih-Wei Tang Hsin-Chi Tsai Ming-Chih Kuo Shu-Hua Chien 《Catalysis Letters》2006,107(1-2):31-37
Three types of supported cobalt catalysts (5% as metal Co loading on SiO2, Al2O3 and TiO2) were prepared by incipient wetness impregnation with aqueous Co(NO3)2·6H2O solution. Then, all catalysts were calcined in air at 400 °C (assigned as 5Co/Si C400, 5Co/Al C400 and 5Co/Ti C400). Their
catalytic activities towards the CO oxidation were studied in a continuous flow micro-reactor. Adsorption of carbon monoxide
(CO) and the co-adsorption of CO/O2 over cobalt oxide were further tested under in situ FT-IR. The results showed that both 5Co/Si C400 and 5Co/Al C400 had higher activity than 5Co/Ti C400. The T50 (50% conversion) for both 5Co/Si C400 and 5Co/Al C400 was reached at temperatures as low as ambient temperature. According
to the in situ FT-IR analysis, the variation in oxidation of CO was interpreted with different mechanisms, i.e., the reaction between adsorbed
CO and lattice oxygen of cobalt oxide, and part of CO2 formation via carbonates on 5Co/Si C400; both types of carbonates are formed on 5Co/Al C400 to promote the CO oxidation;
while both strong adsorption of CO on TiO2 and CO2 on cobalt oxide for 5Co/Ti C400 leads to affect the activity. 相似文献
7.
Si-MCM-41 and Al-MCM-41 supported cobalt oxide catalysts were prepared and characterized by XRD. The surface area, pore size and wall thickness was calculated by applying BET equation and BJH method using nitrogen sorption technique. DR UV-VIS confirm the presence of cobalt oxide as isolated particle in the framework positions of the MCM-41 mesostructure. The vapour phase oxidation of isopropyl benzene with CO2-free air as the oxidant was studied over cobalt oxide supported unwashed and washed Si-MCM-41 and Al-MCM-41 catalyst. Isopropyl benzene conversion increased with increase in temperature from 200 to 300 °C, but at 325 °C it decreased. Formation of coke was noted at all the temperatures. Cumenehydroperoxide, 1,2-epoxyisopropylbenzene, acetophenone and styrene were the products observed in this reaction. Of the products cumenehydroperoxide was found to be more selective over all the catalysts. Both unwashed and washed catalysts were found to have nearly the same activity. Due to more dispersion, the active sites in the latter catalysts compensates its low cobalt oxide content in producing activity equal to the former catalysts. The study of time on stream indicated decrease in conversion due to coke formation. 相似文献
8.
本文采用OM、XRD和SEM,研究了Ti-24Al-14Nb-3V-0.5Mo( at%)合金在700~900℃的氧化行为.合金氧化层主要由TiO2和Al2O3组成.随着氧化温度的升高和时间的延长,TiO2和A12O3颗粒逐渐长大,氧化层逐渐增厚.结果表明,随着温度的升高,合金氧化激活能明显降低.700℃~800℃之间的氧化激活能为205 kJ/mol,800℃~900℃之间的氧化激活能为119 kJ/mol.合金在700℃时具有良好的抗氧化性,800℃和900℃时抗氧化性能大幅降低. 相似文献
9.
The reduction and subsequent reoxidation of isolated vanadate species supported on silica was investigated using temperature-programmed reduction and oxidation, along with in-situ XANES and Raman spectroscopy. Approximately 70–80% of the vanadium was reduced to V3+ after reduction in H2 at temperatures up to 923 K. Upon reduction, the vanadyl oxygen was removed and the three remaining V–O bonds are lengthened by 0.2 Å. The vanadate species are rapidly reoxidized when exposed to O2, with the amount of oxygen uptake matching well with the amount removed during reduction. In-situ Raman spectroscopy during reoxidation in 18O2 showed that significant scrambling occurs between gas phase oxygen and surface oxygen species during the reoxidation of the vanadate species. 相似文献
10.
11.
The kinetics and mechanism of the oxidation of sintered pellets of CoO and Co0.5 Mg0.5 O in air at high temperatures were investigated to find stable heat sources containing 60 Co. The initial stages of oxidation of both materials were nuclei-growth-controlled, i.e. In [1/(1-X)] =ktm . The reaction rate constant for CoO decreased at 800° to 960°C, the temperature where the cobalt oxide spinel decomposed. The reaction-rate constant for decomposition of the mixed oxide was maximum at 700°C and decreased at higher temperatures. This decrease confirmed the validity of the nuclei-growth solid-state reaction-rate equations. 相似文献
12.
Garry Glaspell Hassan M. A. Hassan Ahmed Elzatahry Victor Abdalsayed M. Samy El-Shall 《Topics in Catalysis》2008,47(1-2):22-31
Active gold and palladium nanoparticles supported on a variety of oxides (CeO2, ZrO2, Al2O3, SiO2, MgO and ZnO) were synthesized using laser vaporization and microwave irradiation methods. The catalytic activities for CO
oxidation on the nanoparticle catalysts were evaluated and compared among different oxide supports. The effect of shape on
the catalytic activity is demonstrated by comparing the activities of the Au and Pd catalysts deposited on MgO nanocubes and
ZnO nanobelts. The Au/CeO2 nanoparticles deposited on MgO nanocubes exhibit high catalytic activity and stability. The enhanced catalytic activity is
attributed to the presence of a significant concentration of the corner and edge sites in MgO nanocubes. The Au- and Pd-doped
Mn2O3 nanoparticles show promising results for the low temperature CO oxidation. Several approaches for incorporating the Au and
Pd nanocatalysts within mesoporous oxide supports are presented and discussed. 相似文献
13.
TiO2 and SnO2 were studied as possible supports for HPW in order to produce a new type of sorbent for NO
x
trap applications. SnO2 was synthesised by various inorganic methods while TiO2 was purchased commercially. The sorption capacities and efficiencies depend upon the BET surfaces. Best performances were obtained with support with large pores where the crystalline structure of HPW is maintained. The optimal loading of HPW is ca. 50% with BET surface in the range 20–80 m2g–1. 相似文献
14.
15.
The effect of a reduction promoter, platinum, on the oxidation of a cobalt catalyst was studied. An induction period was observed for the unpromoted catalyst which was absent for the Pt-promoted catalyst. The rate of oxidation was similar for both the Pt-promoted and unpromoted catalyst in the range of degrees of reduction between 50 and 10%. The rate of oxidation of the remainder of metallic cobalt was, however, faster for the platinum promoted catalyst. 相似文献
16.
17.
18.
采用十六胺和不同铈前驱体(硝酸铈铵或硝酸亚铈)分别合成了纳米CeO2(H4和H3),考察了纳米CeO2载体的织构性质对Au-Pd催化剂甲醇部分氧化制氢(POM)性能的影响,用HRTEM、N2吸附、XRD和TPR等对样品进行了表征。结果表明,铈前驱体对载体的性能有较大的影响,以硝酸铈铵为前驱体所制H4载体具有较小的粒径(约5 nm)和平均孔径(5.3 nm)、较大的比表面积(243 m2/g),而硝酸亚铈所制H3载体具有较大的平均孔径(7.9 nm)。POM结果表明,纳米CeO2负载的Au-Pd催化剂具有较好的催化性能,300℃时,Au-Pd/H3的活性和H2选择性分别达100%和59.7%。低温时催化剂的活性和H2选择性为:Au-Pd/H3>Au-Pd/H4,而高温时顺序相反,这是由于低温时催化剂的孔径对反应物和产物的扩散影响较大,高温时催化剂的比表面积和活性组分分散度起主要作用。 相似文献
19.
20.
Cheng-Yuan Tsai Chien-Cheng Lin Avigdor Zangvil Ai-Kang Li 《Journal of the American Ceramic Society》1998,81(9):2413-2420
The oxidation of hot-pressed SiC-particle (SiCp )/zirconia (ZrO2 )/mullite composites with various ZrO2 contents, exposed in air isothermally at 1000° and 1200°C for up to 500 h, was investigated; an emphasis was placed on the effects of the ZrO2 content on the oxidation behavior. A clear critical volume fraction of ZrO2 existed for exposures at either 1000° or 1200°C: the oxidation rate increased dramatically at ZrO2 contents of >20 vol%. The sharp transition in the oxidation rate due to the variation of ZrO2 content could be explained by the percolation theory, when applied to the oxygen diffusivity in a randomly distributed two-phase medium. Morphologically, the composites with ZrO2 contents greater than the critical value showed a large oxidation zone, whereas the composites with ZrO2 contents less than the critical value revealed a much-thinner oxidation zone. The results also indicated that the formation of zircon (ZrSiO4 ) at 1200°C, through the reaction between ZrO2 and the oxide product, could reduce the oxidation rate of the composite. 相似文献