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Title: Time-Resolved X-Ray Absorption Spectroscopy Data for the Study of Chemical Reaction Intermediate States

Abstract

Energy-dispersive X-ray absorption Spectroscopy is an increasingly powerful tool for the investigation of kinetic processes in chemical systems as an element-specific local structure and electronic-state probe. In this paper we present a study of the structural evolution of the inner-sphere electron transfer reaction between [IrCl6]2- and [Co(CN)5]3-. The experimental requirements necessary for the extraction of maximal structural and electronic information are discussed.

Authors:
 [1];  [2];  [3]
  1. Diamond Light Source, Chilton, Didcot, OX11 ODE (United Kingdom)
  2. ISIS Facility, Rutherford Appleton Laboratory, Chilton, Didcot, OX11 0QX (United Kingdom)
  3. School of Chemistry, University of Southampton, Southampton S017 1BJ (United Kingdom)
Publication Date:
OSTI Identifier:
21054760
Resource Type:
Journal Article
Resource Relation:
Journal Name: AIP Conference Proceedings; Journal Volume: 882; Journal Issue: 1; Conference: XAFS13: 13. international conference on X-ray absorption fine structure, Stanford, CA (United States), 9-14 Jul 2006; Other Information: DOI: 10.1063/1.2644682; (c) 2007 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; ABSORPTION SPECTROSCOPY; CARBON NITRIDES; CHEMICAL REACTIONS; COBALT COMPOUNDS; CYANIDES; ELECTRON TRANSFER; ELECTRONIC STRUCTURE; INTERMEDIATE STATE; IRIDIUM CHLORIDES; RADICALS; REACTION KINETICS; TIME RESOLUTION; X-RAY SPECTRA; X-RAY SPECTROSCOPY

Citation Formats

Diaz Moreno, Sofia, Bowron, Daniel T., and Evans, John. Time-Resolved X-Ray Absorption Spectroscopy Data for the Study of Chemical Reaction Intermediate States. United States: N. p., 2007. Web. doi:10.1063/1.2644682.
Diaz Moreno, Sofia, Bowron, Daniel T., & Evans, John. Time-Resolved X-Ray Absorption Spectroscopy Data for the Study of Chemical Reaction Intermediate States. United States. doi:10.1063/1.2644682.
Diaz Moreno, Sofia, Bowron, Daniel T., and Evans, John. Fri . "Time-Resolved X-Ray Absorption Spectroscopy Data for the Study of Chemical Reaction Intermediate States". United States. doi:10.1063/1.2644682.
@article{osti_21054760,
title = {Time-Resolved X-Ray Absorption Spectroscopy Data for the Study of Chemical Reaction Intermediate States},
author = {Diaz Moreno, Sofia and Bowron, Daniel T. and Evans, John},
abstractNote = {Energy-dispersive X-ray absorption Spectroscopy is an increasingly powerful tool for the investigation of kinetic processes in chemical systems as an element-specific local structure and electronic-state probe. In this paper we present a study of the structural evolution of the inner-sphere electron transfer reaction between [IrCl6]2- and [Co(CN)5]3-. The experimental requirements necessary for the extraction of maximal structural and electronic information are discussed.},
doi = {10.1063/1.2644682},
journal = {AIP Conference Proceedings},
number = 1,
volume = 882,
place = {United States},
year = {Fri Feb 02 00:00:00 EST 2007},
month = {Fri Feb 02 00:00:00 EST 2007}
}
  • Desulfation by hydrogen of pre-sulfated Pt(2wt%) BaO(20wt%)/Al2O3 with various sulfur loading (S/Ba = 0.12, 0.31 and 0.62) were investigated by combining H2 temperature programmed reaction (TPRX), x-ray photoelectron spectroscopy (XPS), in-situ sulfur K-edge x-ray absorption near-edge spectroscopy (XANES), and synchrotron time-resolved x-ray diffraction (TR-XRD) techniques. We find that the amount of H2S desorbed during the desulfation in the H2 TPRX experiments is not proportional to the amount of initial sulfur loading. The results of both in-situ sulfur K-edge XANES and TR-XRD show that at low sulfur loadings, sulfates were transformed to a BaS phase and remained in the catalyst, rathermore » than being removed as H2S. On the other hand, when the deposited sulfur level exceeded a certain threshold (at least S/Ba = 0.31) sulfates were reduced to form H2S, and the relative amount of the residual sulfide species in the catalyst was much less than at low sulfur loading. Unlike samples with high sulfur loading (e.g., S/Ba = 0.62), H2O did not promote the desulfation for the sample with S/Ba of 0.12, implying that the formed BaS species originating from the reduction of sulfates at low sulfur loading are more stable to hydrolysis. The results of this combined spectroscopy investigation provide clear evidence to show that sulfates at low sulfur loadings are less likely to be removed as H2S and have a greater tendency to be transformed to BaS on the material, leading to the conclusion that desulfation behavior of Pt BaO/Al2O3 lean NOx trap catalysts is markedly dependent on the sulfation levels.« less
  • Desulfation by hydrogen of presulfated Pt (2 wt %)-BaO(20 wt %)/Al{sub 2}O{sub 3} with various sulfur loading (S/Ba = 0.12, 0.31, and 0.62) were investigated by combining H{sub 2} temperature programmed reaction (TPRX), X-ray photoelectron spectroscopy (XPS), in situ sulfur K-edge X-ray absorption near-edge spectroscopy (XANES), and synchrotron time-resolved X-ray diffraction (TR-XRD) techniques. We find that the amount of H{sub 2}S desorbed during the desulfation in the H{sub 2} TPRX experiments is not proportional to the amount of initial sulfur loading. The results of both in situ sulfur K-edge XANES and TR-XRD show that at low sulfur loadings, sulfates weremore » transformed to a BaS phase and remained in the catalyst rather than being removed as H{sub 2}S. On the other hand, when the deposited sulfur level exceeded a certain threshold (at least S/Ba = 0.31) sulfates were reduced to form H{sub 2}S, and the relative amount of the residual sulfide species in the catalyst was much less than at low sulfur loading. Unlike samples with high sulfur loading (e.g., S/Ba = 0.62), H{sub 2}O did not promote the desulfation for the sample with S/Ba of 0.12, implying that the formed BaS species originating from the reduction of sulfates at low sulfur loading are more stable to hydrolysis. The results of this combined spectroscopy investigation provide clear evidence to show that sulfates at low sulfur loadings are less likely to be removed as H{sub 2}S and have a greater tendency to be transformed to BaS on the material, leading to the conclusion that desulfation behavior of Pt-BaO/Al{sub 2}O{sub 3} lean NO{sub x} trap catalysts is markedly dependent on the sulfation levels.« less
  • No abstract prepared.
  • We present a robust data analysis method of time-resolved x-ray absorption spectroscopy experiments suitable for chemical speciation and structure determination of reaction intermediates. Chemical speciation is done by principal component analysis (PCA) of the time-resolved x-ray absorption near-edge structure data. Structural analysis of intermediate phases is done by theoretical modeling of their extended x-ray absorption fine-structure data isolated by PCA. The method is demonstrated using reduction and reoxidation of Cu-doped ceria catalysts where we detected reaction intermediates and measured fine details of the reaction kinetics. This approach can be directly adapted to many time-resolved x-ray spectroscopy experiments where new rapidmore » throughput data collection and analysis methods are needed.« less