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Title: In Situ XAS Studies on the Structure of the Active Site of Supported Gold Catalysts

Abstract

Gold clusters supported on Al2O3 and TiO2 have been exposed to different mixtures of CO and O2. Their structure has been probed in situ using X-ray absorption spectroscopy (XAS) at the Au L3-edge. In all materials, the dominant phase during catalysis is Au0. Both samples show variations of the electronic structure of the gold clusters with changing reaction conditions as evidenced by changes in the X-ray absorption near-edge (XANES) region. These variations are caused by interaction between the gold clusters and the carbon monoxide present in the gas phase. The gold atoms remain zerovalent throughout all experiments confirming the importance of Au0 for catalytic activity.

Authors:
; ;  [1]; ;  [2];  [3];  [1];  [4]
  1. Molecular Materials Centre, School of Chemical Engineering and Analytical Science, Sackville Street, PO Box 88, Manchester, M60 1QD (United Kingdom)
  2. Laboratoire de Reactivite de Surface, UMR 7609 CNRS, Universite Pierre et Marie Curie, 4 place Jussieu, 75252, Paris, Cedex 05 (France)
  3. Institute for Chemical and Bioengineering, ETH Zurich, 8093 Zurich (Switzerland)
  4. (United Kingdom)
Publication Date:
OSTI Identifier:
21054692
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: 10.1063/1.2644605; (c) 2007 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; ABSORPTION SPECTRA; ABSORPTION SPECTROSCOPY; ALUMINIUM OXIDES; CARBON MONOXIDE; CATALYSIS; CATALYSTS; ELECTRONIC STRUCTURE; GOLD; SOLID CLUSTERS; TITANIUM OXIDES; VARIATIONS; X-RAY SPECTRA; X-RAY SPECTROSCOPY

Citation Formats

Weiher, Norbert, Beesley, Angela M., Tsapatsaris, Nikolaos, Louis, Catherine, Delannoy, Laurent, Bokhoven, Jeroen A. van, Schroeder, Sven L. M., and Molecular Materials Centre, School of Chemistry, Sackville Street, PO Box 88, Manchester, M60 1QD. In Situ XAS Studies on the Structure of the Active Site of Supported Gold Catalysts. United States: N. p., 2007. Web. doi:10.1063/1.2644605.
Weiher, Norbert, Beesley, Angela M., Tsapatsaris, Nikolaos, Louis, Catherine, Delannoy, Laurent, Bokhoven, Jeroen A. van, Schroeder, Sven L. M., & Molecular Materials Centre, School of Chemistry, Sackville Street, PO Box 88, Manchester, M60 1QD. In Situ XAS Studies on the Structure of the Active Site of Supported Gold Catalysts. United States. doi:10.1063/1.2644605.
Weiher, Norbert, Beesley, Angela M., Tsapatsaris, Nikolaos, Louis, Catherine, Delannoy, Laurent, Bokhoven, Jeroen A. van, Schroeder, Sven L. M., and Molecular Materials Centre, School of Chemistry, Sackville Street, PO Box 88, Manchester, M60 1QD. Fri . "In Situ XAS Studies on the Structure of the Active Site of Supported Gold Catalysts". United States. doi:10.1063/1.2644605.
@article{osti_21054692,
title = {In Situ XAS Studies on the Structure of the Active Site of Supported Gold Catalysts},
author = {Weiher, Norbert and Beesley, Angela M. and Tsapatsaris, Nikolaos and Louis, Catherine and Delannoy, Laurent and Bokhoven, Jeroen A. van and Schroeder, Sven L. M. and Molecular Materials Centre, School of Chemistry, Sackville Street, PO Box 88, Manchester, M60 1QD},
abstractNote = {Gold clusters supported on Al2O3 and TiO2 have been exposed to different mixtures of CO and O2. Their structure has been probed in situ using X-ray absorption spectroscopy (XAS) at the Au L3-edge. In all materials, the dominant phase during catalysis is Au0. Both samples show variations of the electronic structure of the gold clusters with changing reaction conditions as evidenced by changes in the X-ray absorption near-edge (XANES) region. These variations are caused by interaction between the gold clusters and the carbon monoxide present in the gas phase. The gold atoms remain zerovalent throughout all experiments confirming the importance of Au0 for catalytic activity.},
doi = {10.1063/1.2644605},
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}
}
  • Uniform Au nanoparticles (~2 nm) with narrow size-distribution (standard deviation: 0.5–0.6 nm) supported on both hydroxylated (Fe_OH) and dehydrated iron oxide (Fe_O) have been prepared by either deposition-precipitation (DP) or colloidal-deposition (CD) methods. Different structural and textural characterizations were applied to the dried, calcined and used gold-iron oxide samples. The transmission electron microscopy (TEM) and high-resolution TEM (HRTEM) described the high homogeneity in the supported Au nanoparticles. The ex-situ and in-situ X-ray absorption fine structure (XAFS) characterization monitored the electronic and short-range local structure of active gold species. The synchrotron-based in-situ X-ray diffraction (XRD), together with the corresponding temperature-programmed reductionmore » by hydrogen (H₂-TPR), indicated a structural evolution of the iron-oxide supports, correlating to their reducibility. An inverse order of catalytic activity between DP (Au/Fe_OH < Au/Fe_O) and CD (Au/Fe_OH > Au/Fe_O) was observed. Effective gold-support interaction results in a high activity for gold nanoparticles, locally generated by the sintering of dispersed Au atoms on the oxide support in the DP synthesis, while a hydroxylated surface favors the reactivity of externally introduced Au nanoparticles on Fe_OH support for the CD approach. This work reveals why differences in the synthetic protocol translate to differences in the catalytic performance of Au/FeO x catalysts with very similar structural characteristics in CO oxidation.« less
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  • The techniques of energy dispersive EXAFS (EDE), diffuse reflectance Fourier transform infrared spectroscopy (DRIFTS) and mass spectrometry (MS) have been combined to study the structure and function of an oxide supported metal catalyst, namely 5 wt% Rh/Al2O3. Using a FreLoN camera as the EDE detector and a rapid-scanning IR spectrometer, experiments could be performed with a repetition rate of 50 ms. The results show that the nature of the rhodium centers is a function of the partial pressures of the reacting gases (CO and NO) and also temperature. This combination of gases oxidizes metallic rhodium particles to Rh(CO)2 at roommore » temperature. The proportion of the rhodium adopting this site increases as the temperature is raised (up to 450 K). Above that temperature the dicarbonyl decomposes and the metal reclusters. Once this condition is met, catalysis ensues. Gas switching techniques show that at 573 K with NO in excess, the clusters can be oxidized rapidly to afford a linear nitrosyl complex; re-exposure to CO also promotes reclustering and the CO adopts terminal (atop) and bridging (2-fold) sites.« less