962 resultados para Ce^3
Resumo:
In this work we propose the study of the spectroscopy properties and the energy level location of Ce(3+) and Pr(3+) in Gd(2)O(2)S, along with the effects of Ce(4+) (Ce(2)O(2)S(2)) incorporation in Gd(2)O(2)S and Gd(2)O(2)S: Pr(3+) in order to understand the formation and position of the associated defects energy levels in relation to the band structure of Gd(2)O(2)S and Pr(3+) energy levels. Ce-, Pr(3+)-doped and Pr(3+), Ce-doped Gd(2)O(2)S were prepared by the sulfidization of a basic gadolinium carbonate with S(8) using H(2)/N(2) (3.0/97.0%) and air during the firing of the precursor. Samples were analyzed by X-ray diffraction in order to guarantee the formation of the Gd(2)O(2)S single phase. Diffuse reflectance spectroscopy and luminescent measurements (emission/excitation) were used to locate Ce(3+), Pr(3+) and defects energy levels in relation to the band structure of Gd(2)O(2)S. (C) 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Resumo:
The redox property of ceria is a key factor in the catalytic activity of ceria-based catalysts. The oxidation state of well-defined ceria nanocubes in gas environments was analysed in situ by a novel combination of near-ambient pressure X-ray Photoelectron Spectroscopy (XPS) and high-energy XPS at a synchrotron X-ray source. In situ high-energy XPS is a promising new tool to determine the electronic structure of matter under defined conditions. The aim was to quantitatively determine the degree of cerium reduction in a nano-structured ceria-supported platinum catalyst as a function of the gas environment. To obtain a non-destructive depth profile at near-ambient pressure, in situ high-energy XPS analysis was performed by varying the kinetic energy of photoelectrons from 1 to 5 keV, and, thus, the probing depth. In ceria nanocubes doped with platinum, oxygen vacancies formed only in the uppermost layers of ceria in an atmosphere of 1 mbar hydrogen and 403 K. For pristine ceria nanocubes, no change in the cerium oxidation state in various hydrogen or oxygen atmospheres was observed as a function of probing depth. In the absence of platinum, hydrogen does not dissociate and, thus, does not lead to reduction of ceria.
Resumo:
(Sm~(3+),Ce~(3+)Gd~(3+).Sb~(3+)(Sm~(3+)+Ce~(3+)Sm~(3+)+Gd~(3+),Sm~(3+)+Sb~(3+))(Sm~(3+)+Gd~(3+)+Ce~(3+)).Sm~(3+)Ce~(3+),Gd~(3+)Sb~(3+)Ce~(3+)+Gd~(3+)Sm~(3+)
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A combined electrochemical method and X-ray photo electron spectroscopy (XPS) has been utilized to understand the Pd(2+)/CeO(2) interaction in Ce(1-x)Pd(x)O(2-delta) (x = 0.02). A constant positive potential (chronoamperometry) is applied to Ce(0.98)Pd(0.02)O(2-delta) working electrode which causes Ce(4+) to reduce to Ce(3+) to the extent of similar to 35%, while Pd remains in the +2 oxidation state. Electrochemically cycling this electrode between 0.0-1.2 V reverts back to the original state of the catalyst. This reversibility is attributed to the reversible reduction of Ce(4+) to Ce(3+) state. CeO(2) electrode with no metal component reduces to CeO(2-y) (y similar to 0.4) after applying 1.2 V which is not reversible and the original composition of CeO(2) cannot be brought back in any electrochemical condition. During the electro-catalytic oxygen evolution reaction at a constant 1.2 V for 1000 s, Ce(0.98)Pd(0.02)O(2-delta) reaches a steady state composition with Pd in the +2 states and Ce(4+) : Ce(3+) in the ratio of 0.65 : 0.35. This composition can be denoted as Ce(0.63)(4+)Ce(0.35)(4+)Pd(0.02)O(2-delta-y) (y similar to 0.17). When pure CeO(2) is put under similar electrochemical condition, it never reaches the steady state composition and reduces almost to 85%. Thus, Ce(0.98)Pd(0.02)O(2-delta) forms a stable electrode for the electro-oxidation of H(2)O to O(2) unlike CeO(2) due to the metal support interaction.
Resumo:
60mm110mmCeLu1.6Y0.4SiO5LYSO,LSO,LYSO.LYSO,YLSO.Ce^34f^15d^1.Ce^3,Gaussian,395nm418nmCe1,435nmCe2
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CeLuSi2O7(CeLPS)xC21m(110)CeLPSCeLPS302349nmCe^3+4f^15d^1Ce^3+Gaussian384407nm
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266nmCe^3YAPCeYAPCe182nsCe^30106
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ABLa(PO_4)_2900 LaPO_4RE~(3+)(RE = Ce,Tb,Dy)ABLa(PO_4)_2Ce~(3+)Tb~(3+)Rc(dd)ABLa(PO_4)_2Ce~(3+)Tb~(3+)Ce~(3+)Ce~(3+)Ce~(3+)Tb~(3+)LaPO_4Ce~(3+) Ce~(3+)Ce~(3+) Tb~(3+)Ce~(3+) Ce~(3+)ABLa(PO_4)_2:Ce,TbTb~(3+)ABLa(PO_4)_2Ce~(3+)Ce~(3+)-Tb~(3+)Ce~(3+)-Dy~(3+)ABLa(PO_4)_2:CeTbCe~(3+)Tb~(3+)B_2O_3Dy~(3+)SiO_2NH_4ClCe~(3+)Tb~(3+)0.20.50.080.2B_2O_3Dy~(3+)SiO_2NH_4Cl
Resumo:
In view of the growing interest in endohedral lanthanide fullerenes, Ce, as a typical +4 oxidation state lanthanide element, has been systematically studied. The synthesis, extraction and electronic structure of Ce@C-2n are investigated. Soot containing Ce@C-2n was synthesized in high yield by carbonizing CeO2-containing graphite rods and are back-burning the CeC2-enriched cathode deposit in a DC are plasma apparatus. Ce@C-2n, dominated by Ce@C-82, can be efficiently extracted from the insoluble part of the soot after toluene Soxhlet extraction by pyridine at high temperature and high pressure in a closed vessel. About 60% Ce@C-2n (2n = 82,80,78,76) and 35% Ce@C-82 can be enriched in the pyridine extract. This fact is identified by desorption electron impact mass spectrometry (DEI MS). The electronic structure of Ce@C-2n is analyzed by using X-ray photoemission spectroscopy (XPS) of pyridine-free film. It is suggested that the encapsulated Ce atom is in a charge state close to +3 and was effectively protected from reaction with water and oxygen by the enclosing fullerene cage. Unlike theoretical expectation, the electronic state of Ce@C-82 is formally described as Ce+3@C-82(3-). (C) 1997 Elsevier Science Ltd.
Resumo:
Eu-TbCe-Yb.Ce~(3+)Eu~(3+),.1 1.1 CaF_2,SrF_2,BaF_2,NH_4HF_2,EuF_3CeF_3Eu_2O_3(99.95%)CeO_2(99.99%).1.2 MF_2:Eu,Ce(MF_2:X%CeF_2,y%EuF_3;X=1,y=0,0.1,0.3,0.5,1;X=0,0.05,0.1,0.3,0.5,y=1),,(
Resumo:
,,,.,SumaokaCe~(3+)3,5-(cAMP),.3,5-3,5-(cGMP),.(HPLC)(NMR)cAMPcGMP,,,.
Resumo:
La_4(P_2O_7)_3;Ce,Gd,Tb.X,La_4(P_2O_7)_3Ce~(3+),Ce~(3+)Gd~(3+),,(La_(0.64)Ce_(0.3)Gd_(0.06)_4(P_2O_7)_3(La_(0.7)Ce_(0.3)_4(P_2O_7)3(La_(0.94)Gd_(0.06)_4(P_2O_7)_3.,Ce~(3+)Tb~(3+)~9,Tb~(3+).,Gd~(3+)Tb~(3+),(La_(0.80)Gd_(0.06)Tb_(0.14)_4(P_2O_7)_3(La_(0.86)Tb_(0.14)_4(P_2O_7)3.Ce,GdTb,Gd~(3+),Tb~(3+),
Resumo:
Ce~(3+)4f-5d,,Ce~(3+)5d-4f,5dCe~(3+),Ce~(3+)Tb~(3+),Ce~(3+)Tb~(3+),LaPO_4:Ce,Tb,Ce~(3+)Tb~(3+),