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41.
42.
《Angewandte Chemie (International ed. in English)》2017,56(42):13041-13046
Studies with a series of metal/ceria(111) (metal=Co, Ni, Cu; ceria=CeO2) surfaces indicate that metal–oxide interactions can play a very important role for the activation of methane and its reforming with CO2 at relatively low temperatures (600–700 K). Among the systems examined, Co/CeO2(111) exhibits the best performance and Cu/CeO2(111) has negligible activity. Experiments using ambient pressure X‐ray photoelectron spectroscopy indicate that methane dissociates on Co/CeO2(111) at temperatures as low as 300 K—generating CHx and COx species on the catalyst surface. The results of density functional calculations show a reduction in the methane activation barrier from 1.07 eV on Co(0001) to 0.87 eV on Co2+/CeO2(111), and to only 0.05 eV on Co0/CeO2−x (111). At 700 K, under methane dry reforming conditions, CO2 dissociates on the oxide surface and a catalytic cycle is established without coke deposition. A significant part of the CHx formed on the Co0/CeO2−x (111) catalyst recombines to yield ethane or ethylene. 相似文献
43.
For CeO2 or M‐doped CeO2 catalysts, reliable energetics associated with surface reactivity requires accurate representation of oxidized and reduced metal states. Density functional theory (DFT) is used extensively for metals and metal oxides; however, for strongly correlated electron materials, conventional DFT fails to predict both qualitative and quantitative properties. This is the result of a localized electron self‐interaction error that is inherit to DFT. DFT+U has shown promise in correcting energetic errors due to the self‐interaction error, however, its transferability across processes relevant to surface catalysis remains unclear. Hybrid functionals, such as HSE06, can also be used to correct this self‐interaction error. These hybrid functionals are computationally intensive, and especially demanding for periodic surface slab models. This perspective details the challenges in representing the energetics of M‐doped ceria catalyzed processes and examines using DFT extensions to model the localized electronic properties. © 2013 Wiley Periodicals, Inc. 相似文献
44.
W.Y. Hernández O.H. Laguna M.A. Centeno J.A. Odriozola 《Journal of solid state chemistry》2011,184(11):3014-3020
Ce0.9M0.1O2−δ mixed oxides (M=La, Eu and Gd) were synthesized by coprecipitation. Independent of the dopant cation, the obtained solids maintain the F-type crystalline structure, characteristic of CeO2 (fluorite structure) without phase segregation. The ceria lattice expands depending on the ionic radii of the dopant cation, as indicated by X-ray diffraction studies. This effect also agrees with the observed shift of the F2g Raman vibrational mode. The presence of the dopant cations in the ceria lattice increases the concentration of structural oxygen vacancies and the reducibility of the redox pair Ce4+/Ce3+. All synthesized materials show higher catalytic activity for the CO oxidation reaction than that of bare CeO2, being Eu-doped solid the one with the best catalytic performances despite of its lower surface area. 相似文献
45.
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47.
Malta L. F. B. Cafffarena V. R. Medeiros M. E. Ogasawara T. 《Journal of Thermal Analysis and Calorimetry》2004,75(3):901-910
Doped ceria was studied in the last 20 years as a solid electrolyte capable of replacing stabilized zirconia in fuel cells.
Nevertheless, one of the problems concerned with the application of this material is the joint presence of the Ce(III) and
Ce(IV) in the ceria sublattice, mainly under low partial pressure of oxygen. TG and DTA measurements were performed in order
to verify non-stoichiometric character for cerias hydrothermally treated under reflux and in autoclave. X-ray powder diffraction
was used to observe long-range structural evolution varying time and temperature of reaction and the type of hydrothermal
synthesis. Finally, scanning electron microscopy (SEM) gave the temperature influence for powder morphology. Those techniques
pointed out that: i) reaction temperature is not important for converting Ce3+ to Ce4+; ii) testing the reaction time parameter, it is observed quite complete oxidation for the 2-12 h range; and iii) the type of
hydrothermal synthesis parameter influences the crystallinity and non-stoichiometric character of products.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
48.
François Cheviré Charles F. Baker Olivier Larcher Christophe Colbeau-Justin 《Journal of solid state chemistry》2006,179(10):3184-3190
A new fluorite-type solid solution domain has been evidenced in the system (1−x) CeO2−x/7 Y6WO12□2 using the amorphous citrate route. All the studied phases (0?x?1) crystallize in a cubic-type symmetry. Diffuse reflectance spectra reveal a strong optical absorption between 380 and 400 nm. All substituted compositions spectral selectivities are estimated suitable for application as inorganic UV absorbers. The non linear variation observed in the optical gap values between Y6WO12 and CeO2 is attributed to the presence of the cerium 4f-block band. Additionally, Time Resolved Microwave Conductivity (TRMC) experiment and phenol photodegradation analyses carried out on the Ce0.81Y0.16W0.03O1.95□0.05 (x=0.19) composition do not indicate any photocalatytic activity for this material. 相似文献
49.
Summary Molybdena modified pure as well as sulfated ceria systems have been studied with a view to investigate their structure, surface
acidic properties and catalytic behavior for cyclohexanol decomposition reaction. The characteristics of the modified systems
were obtained from XRD measurements and acid structural properties from Temperature Programmed Desorption (TPD) of ammonia. 相似文献
50.
P. Kumar 《辐射效应与固体损伤》2013,168(4):258-264
The formation of nano-size hillocks and simple and complex craters was observed as a result of ion–surface collisions with a lithium niobate single crystal on proton implantation. The low-energy ion implantation process is considered as a controllable and versatile tool for surface and near-surface modifications down to an atomic scale as an alternative to the swift heavy ion irradiation effect. Lithium niobate samples implanted by proton ions with a low energy of 120 keV at various fluences (1015 and 1016 protons/cm2) were studied using atomic force microscopy (AFM). The images of surface modification appear as simple and complex crater formation in the case of incident ions at normal to the surface. Varying the angle of incidence to θ=30° with respect to the normal to the surface, hillocks and multi-hillocks were observed. The complex craters with central uplifted, cone-shaped hillocks with a height of up to 4.3 nm are surrounded by low-height (1 nm) rims. The hillock height varies from a few nanometers to 16 nm with the basal diameter from 200 to 340 nm depending on the ion implantation conditions. The complex crater and hillock formation on the lithium niobate sample surface at the collision spot with the impact of incident angle is discussed. 相似文献