Properties of CeO2and Ce1-xZrxO2Nanoparticles:  X-ray Absorption Near-Edge Spectroscopy, Density Functional, and Time-Resolved X-ray Diffraction Studies

2003 ◽  
Vol 107 (15) ◽  
pp. 3535-3543 ◽  
Author(s):  
José A. Rodriguez ◽  
Jonathan C. Hanson ◽  
Jae-Yong Kim ◽  
Gang Liu ◽  
Ana Iglesias-Juez ◽  
...  
Keyword(s):  
Density Functional ◽  
X Ray Diffraction ◽  
Time Resolved ◽  
X Ray ◽  
X Ray Absorption

scholarly journals Characterization of Mixed-Metal Oxides Using Synchrotron-Based Time-Resolved x-ray Diffraction and x-ray Absorption Spectroscopy

1999 ◽  
Vol 590 ◽  
Author(s):  
José A. Rodriguez ◽  
Jonathan C. Hanson ◽  
Joaquín L. Brito ◽  
Amitesh Maiti
Keyword(s):  
Metal Oxides ◽  
Density Functional ◽  
Chemical Properties ◽  
Local Symmetry ◽  
Mixed Metal Oxides ◽  
X Ray Diffraction ◽  
Time Resolved ◽  
X Ray ◽  
Mixed Metal ◽  
X Ray Absorption

ABSTRACTExperiments are described showing the utility of synchrotron-based time-resolved x-ray diffraction (TR-XRD) and x-ray absorption near-edge spectroscopy (XANES) for characterizing the physical and chemical properties of mixed-metal oxides that contain Mo and a second transition metal (Fe, Co or Ni). TR-XRD was used to study the transformations that occur during the heating of a FeMoO4/Fe2(MoO4)3 mixture and the α⇒β phase transitions in CoMoO4 and NiMoO4. The Mo LII- and O K-edges in XANES are very useful for probing the local symmetry of Mo atoms in mixed-metal oxides. The results of XANES and density-functional calculations (DMo13, DFT-GGA) show large changes in the splitting of the empty Mo 4d levels when going from tetrahedral to octahedral coordinations. XANES is very useful for studying the reaction of H2, H2S and SO2 with the mixed-metal oxides. Measurements at the S K-edge allow a clear identification of S, SO2, SO3 or SO4 on the oxide surfaces. Changes in the oxidation state of molybdenum produce substantial shifts in the position of the Mo LII- and MIII-edges.

A dispenser–reactor apparatus applied forin situXAS monitoring of Pt nanoparticle formation

2015 ◽  
Vol 22 (3) ◽  
pp. 736-744 ◽  
Author(s):  
Jocenir Boita ◽  
Marcus Vinicius Castegnaro ◽  
Maria do Carmo Martins Alves ◽  
Jonder Morais
Keyword(s):  
Photoelectron Spectroscopy ◽  
Metallic Nanoparticles ◽  
Pt Nanoparticles ◽  
Lattice Parameter ◽  
X Ray Diffraction ◽  
Time Resolved ◽  
X Ray ◽  
Two Stages ◽  
X Ray Absorption

In situtime-resolved X-ray absorption spectroscopy (XAS) measurements collected at the PtL3-edge during the synthesis of Pt nanoparticles (NPs) in aqueous solution are reported. A specially designed dispenser–reactor apparatus allowed for monitoring changes in the XAS spectra from the earliest moments of Pt ions in solution until the formation of metallic nanoparticles with a mean diameter of 4.9 ± 1.1 nm. By monitoring the changes in the local chemical environment of the Pt atoms in real time, it was possible to observe that the NPs formation kinetics involved two stages: a reduction-nucleation burst followed by a slow growth and stabilization of NPs. Subsequently, the synthesized Pt NPs were supported on activated carbon and characterized by synchrotron-radiation-excited X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and extended X-ray absorption fine structure (EXAFS). The supported Pt NPs remained in the metallic chemical state and with a reduced size, presenting slight lattice parameter contraction in comparison with the bulk Pt values.

Properties of Pure and Sulfided NiMoO4 and CoMoO4 Catalysts: Tpr, Xanes and Time-Resolved XRD Studdzs

1997 ◽  
Vol 497 ◽  
Author(s):  
S. Chaturvedi ◽  
J. A. Rodriguez ◽  
J. C. Hanson ◽  
A. Albornoz ◽  
J. L. Brito
Keyword(s):  
Electronic Properties ◽  
X Ray Diffraction ◽  
Time Resolved ◽  
Direct Transformation ◽  
X Ray ◽  
Β Phase ◽  
Structural And Electronic Properties ◽  
X Ray Absorption ◽  
Kinetics Of ◽  
Cobalt And Nickel

ABSTRACTX-ray absorption near-edge spectroscopy (XANES) was used to characterize the structural and electronic properties of a series of cobalt- and nickel-molybdate catalysts (AMoO4.nH20, α-AMoO4, β-AMoO4; A= Co or Ni). The results of XANES indicate that the Co and Ni atoms are in octahedral sites in all these compounds, while the coordination of Mo varies from octahedral in the a-phases to tetrahedral in the β-phases and hydrate. Time-resolved x-ray diffraction shows a direct transformation of the hydrates into the β-AMoO4 compounds (following a kinetics of first order) at temperatures between 200 and 350 °C. This is facilitated by the similarities that the AMoO4.nH20 and β-AMoO4 compounds have in their structural and electronic properties. The molybdates react with H 2 at temperatures between 400 and 600 °C, forming gaseous water and oxides in which the oxidation state of Co and Ni remains +2 while that of Mo is reduced to +5 or +4. After exposing α-NiMoO4 and P-NiMoO4 to H2S, both metals get sulfided and a NiMoSx phase is formed. For the β phase of NiMoO4 the sulfidation of Mo is more extensive than for the a phase, making the former a better precursor for catalysts of hydrodesulfurization reactions.

Phase Transition Analysis between LiFePO4and FePO4by In-Situ Time-Resolved X-ray Absorption and X-ray Diffraction

2013 ◽  
Vol 160 (5) ◽  
pp. A3061-A3065 ◽  
Author(s):  
Yuki Orikasa ◽  
Takehiro Maeda ◽  
Yukinori Koyama ◽  
Taketoshi Minato ◽  
Haruno Murayama ◽  
...  
Keyword(s):  
Phase Transition ◽  
X Ray Diffraction ◽  
Transition Analysis ◽  
Time Resolved ◽  
X Ray ◽  
X Ray Absorption

scholarly journals Expanding the Mechanochemical Toolbox: Combining X-Ray Absorption Spectroscopy and Scattering for in Situ Time-Resolved Monitoring of Gold Nanoparticle Mechanosynthesis

2020 ◽  
Author(s):  
Paulo F M de Oliveira ◽  
Adam Michalchuk ◽  
Ana de Oliveira Guilherme Buzanich ◽  
Ralf Bienert ◽  
Roberto M. Torresi ◽  
...  
Keyword(s):  
Absorption Spectroscopy ◽  
Electronic Materials ◽  
Early Stage ◽  
X Ray Diffraction ◽  
Time Resolved ◽  
Subsequent Formation ◽  
X Ray ◽  
Detection Capabilities ◽  
X Ray Absorption

<div>The development of time-resolved in situ approaches for monitoring mechanochemical</div><div>transformations has revolutionized the field of mechanochemistry. Currently, the established in</div><div>situ approaches greatly limit the scope of investigations that are possible. Here we develop a new</div><div>approach to simultaneously follow the evolution of bulk atomic and electronic structure during a</div><div>mechanochemical synthesis. This is achieved by coupling two complementary synchrotron-based</div><div>X-ray methods: X-ray absorption spectroscopy and X-ray diffraction. We apply this method to</div><div>investigate the bottom-up mechanosynthesis of technologically important Au nanoparticles in the</div><div>presence of three different reducing agents. Moreover, we demonstrate how X-ray absorption</div><div>spectroscopy offers unprecedented insight into the early stage generation of growth species (e.g.</div><div>monomers and clusters), which lead to the subsequent formation of nanoparticles. These</div><div>processes are beyond the detection capabilities of diffraction methods. The approach is general,</div><div>and not limited to monitoring NP mechanosynthesis. This combined X-ray approach paves the</div><div>way to new directions in mechanochemical research of advanced electronic materials.</div>

Soft X-ray excited colour-centre luminescence and XANES studies of calcium oxide

2007 ◽  
Vol 85 (10) ◽  
pp. 853-858 ◽  
Author(s):  
JY Peter Ko ◽  
Franziskus Heigl ◽  
Yun Mui Yiu ◽  
Xing-Tai Zhou ◽  
Tom Regier ◽  
...  
Keyword(s):  
Calcium Oxide ◽  
Density Functional ◽  
X Rays ◽  
Colour Centre ◽  
Time Resolved ◽  
Edge Structure ◽  
Colour Centres ◽  
X Ray ◽  
Optical Luminescence ◽  
X Ray Absorption

In this study, we show that colour centres can be produced by irradiating calcium oxide with soft X-rays from a synchrotron radiation source. Using the X-ray excited optical luminescence (XEOL) technique, two colour centres, F-centre, and F+-centre can be identified. These colour centres emit photons at characteristic wavelengths. In addition, by performing time-resolved XEOL (TRXEOL), we are able to reveal timing and decay characteristics of the colour centres. We also present X-ray absorption near-edge structure (XANES) spectra collected across oxygen K-edge, calcium L3,2-edge, and calcium K-edge. Experimental results are compared with density functional theory (DFT) calculations.Key words: calcium oxide, colour centre, synchrotron, X-ray excited optical luminescence, X-ray absorption near-edge structure.

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