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Koningsberger, D.C.; Mojet, Barbara; Dorssen, G.E. van; Ramaker, David E.

doi:10.1023/a:1019105310221

Cited by 499 publications

(581 citation statements)

References 26 publications

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“…25 The absorption data were pre-edge and background-subtracted by means of standard procedures. 3 The spectra were normalized on the height of the edge-step at 50 eV over the edge. Multiple shell fitting was performed in R-space (3.2 < k < 13 Å -1 , 1.6 < R < 3.2 Å) using k weightings of 1 and 3.…”

Section: Discussionmentioning

confidence: 99%

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Analysis of in situ EXAFS data of supported metal catalysts using the third and fourth cumulant

Bus

Miller²,

Kropf

et al. 2006

Phys. Chem. Chem. Phys.

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[DO NOT ALTER/DELETE THIS TEXT]X-ray absorption spectra of supported Pt catalysts with various Pt cluster sizes were collected between 77 and 673 K, in inert and hydrogen atmospheres. When analyzing these spectra with the standard EXAFS equation a Pt-Pt bond contraction and a large increase in the inner potential correction were observed with increasing temperature.These errors are up to 0.08 Å and 10 eV for clusters of 1 nm in diameter. They were corrected by including the third and fourth cumulants as fit parameters. Fit guidelines were developed to analyze EXAFS data of supported metal catalysts collected at elevated temperatures, allowing for asymmetry and broadening or sharpening of the pair distribution function. These comprise fixing fit parameters, using different k-weightings, and identifying trends in series of experiments. By fitting the EXAFS spectra using these guidelines, it was determined that in small Pt clusters the Pt-Pt bond is 0.10 Å shorter than in bulk Pt. These contracted bonds relax to distances near that of bulk Pt upon hydrogen chemisorption.2

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Section: Discussionmentioning

confidence: 99%

“…These parameters are typical for small Pt clusters. The functions were calculated in the multiple shell analysis routine of the XDAP software package, 3 by fixing the values of all fit parameters. The functions were analyzed without including the higher-order cumulants.…”

Section: Theoretical Spectramentioning

confidence: 99%

Analysis of in situ EXAFS data of supported metal catalysts using the third and fourth cumulant

Bus

Miller²,

Kropf

et al. 2006

Phys. Chem. Chem. Phys.

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“…[10] The AXAFS is related to the orbital energy through the resonant scattering condition of the photoelectron, that is, the kinetic energy of the photoelectron is equal to the kinetic energy of the bound electron (only the deeper localised valence orbitals are relevant for the AXAFS scattering). [34] The effects determining the FT AXAFS peak can be described using the muffin-tin approximation to approximate the embedded atom potential. Within the muffin-tin approximation, the potential is flat and zero in the interstitial region (R > R mt ) and otherwise equal to the sum of overlapping, spherically symmetrical potentials (R < R mt ).…”

Section: Discussionmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

“…[34] This led to the normalised oscillatory part of the XAFS data, for which all contributions to the spectrum, including the AXAFS, were maximised. [34] The EXAFS data analysis program XDAP allows one to perform multiple-shell fitting in R-space by minimising the residuals between both the absolute and the imaginary part of the Fourier transforms of the data and the fit. R-space fitting has important advantages compared to the usually applied fitting in k-space and is extensively discussed in a paper by Koningsberger et al [34] All contributions were fitted simultaneously in R-space with concomitant inspection of the FT of the difference file and calculated fit of each individual contribution.…”

Section: Methodsmentioning

confidence: 99%

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Application of AXAFS Spectroscopy to Transition‐Metal Oxides: Influence of the Nearest and Next Nearest Neighbour Shells in Vanadium Oxides

Keller

Weckhuysen

Koningsberger

2007

Chemistry A European J

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IntroductionMany parameters affect the catalytic properties of transition-metal oxide catalysts, for example, metal oxide loading, pre-treatment conditions, molecular structure, electronic structure, and the nature of the supporting oxide. [1][2][3][4][5][6][7] Various researchers have investigated the activities and selectivities of metal oxide catalysts. However, little is known about the parameters that are truly responsible for the catalytic action of transition-metal oxides.To study the effect of the support on the catalytic performance, one has to find a tool that is capable of probing the influence of the local environment (e.g., the support or promoters) on the properties of the catalytically active species, that is, a metal particle or metal oxide cluster. Metal-A C H T U N G T R E N N U N G (oxide)-support interactions can be ascribed to a structural (particle/cluster size and shape) effect, but can also have an electronic origin. For supported metal particles, the effect of the support on the catalytic properties has been determined by several techniques, for example, XPS, FT-IR analysis of adsorbed CO, and newly developed delta XANES and atomic XAFS (AXAFS) techniques. [8][9][10][11][12][13][14][15] In particular, the application of AXAFS has, in our opinion, led to a better understanding of metal-support interaction effects. [8,[15][16][17] AXAFS is sensitive to changes in the potential around the X-ray absorbing atom. The potential field around an atom is mainly determined by the first and second coordination spheres. O Grady et al. have shown for Pt/Ru alloys that the AXAFS intensity changes systematically with the composition of the alloy. [18] Thus, when the number of Ru atoms around a Pt atom increases, the intensity of the FT AXAFS peak increases and the peak centroid shifts to lower values of R. Comparison of these effects with the effects observed for a Pt electrode as a function of the applied voltage suggests that the first coordination shell of the Pt in the Pt/Ru alloy influences the electronic properties (inter-A C H T U N G T R E N N U N G atomic potential) of the Pt atom. [18,19] The effect of changes in the coordination around the absorber atom has been further illustrated for Pt by van Dorssen et al., who compared the AXAFS of a Pt foil with that of bulk Na 2 Pt(OH) 6 . The AXAFS intensity was found to be significantly higher in the Abstract: The influence of changes in coordination number, interatomic distances, and oxidation state on the intensity and centroid position of the Fourier transform (FT) of the atomic X-ray absorption fine structure (AXAFS) peak of vanadium oxide bulk model compounds and aluminasupported vanadium oxide clusters has been investigated. Using Na 3 VO 4 and V 2 O 5 as model compounds, it has been shown that the nearest neighbour shells have a pronounced influence on the AXAFS intensity; specifically, a 40 % decrease in intensity was observed between these two compounds. Secondly, the influence of partial reduction of the vanadium oxide species has been dete...

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Catalyst Characterization – Heterogeneous

Knözinger

Taglauer

2002

Encyclopedia of Catalysis

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Physical and chemical properties of solid catalysts critically determine their performance. This review summarizes the techniques which permit analysis and determination of these properties. The physical principle and the potential of each technique is briefly discussed and characteristic examples are given. The techniques mentioned include those for determining surface area and porosity, x‐ray diffraction and absorption, electron microscopy, scanning probe microscopy, vibrational spectroscopies (infrared and Raman), nonlinear optical spectroscopy, neutron diffraction and inelastic scattering, nuclear spectroscopy (spectroscopies and nuclear magnetic resonance), electron spectroscopy (Auger and photoelectron spectroscopy), ion scattering spectroscopy, optical absorption and luminescence spectroscopy, electron paramagnetic resonance, and thermoanalytical methods. The review concludes with a brief description of the determination of mechanical strength of solid catalysts.

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Cited by 499 publications

References 26 publications

Analysis of in situ EXAFS data of supported metal catalysts using the third and fourth cumulant

Analysis of in situ EXAFS data of supported metal catalysts using the third and fourth cumulant

Application of AXAFS Spectroscopy to Transition‐Metal Oxides: Influence of the Nearest and Next Nearest Neighbour Shells in Vanadium Oxides

Catalyst Characterization – Heterogeneous

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