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Title: A Cu/Pt Near-Surface Alloy for Water-Gas Shift Catalysis.

Abstract

The research described in this product was performed in part in the Environmental Molecular Sciences Laboratory, a national scientific user facility sponsored by the Department of Energy's Office of Biological and Environmental Research and located at Pacific Northwest National Laboratory. The primary route to hydrogen production from fossil fuels involves the water-gas shift (WGS) reaction, and an improvement in the efficiency of WGS catalysts could therefore lead to a major leap forward in the realization of hydrogen economy. On the basis of a combination of high-resolution scanning tunneling microscopy, X-ray photoelectron spectroscopy, and density functional theory (DFT) calculations, we suggest the existence of a new thermodynamically stable Cu/Pt near-surface alloy (NSA). Temperature-programmed desorption and DFT reveal that this Cu/Pt NSA binds CO significantly more weakly than does Pt alone, thereby implying a considerable reduction in the potential for CO poisoning of the Cu/Pt NSA surface as compared to that of pure Pt. In addition, DFT calculations show that this Cu/Pt NSA is able to activate H2O easily, which is the rate-determining step for the WGS on several metal surfaces, and, at the same time, to bind the products of that reaction and formate intermediates rather weakly, thus avoiding possible poisoningmore » of the catalyst surface. The Cu/Pt NSA is thus a promising candidate for an improved WGS catalyst.« less

Authors:
; ; ; ; ; ; ;
Publication Date:
Research Org.:
Pacific Northwest National Laboratory (PNNL), Richland, WA (US), Environmental Molecular Sciences Laboratory (EMSL)
Sponsoring Org.:
USDOE
OSTI Identifier:
989063
DOE Contract Number:
AC05-76RL01830
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of the American Chemical Society, 129(20):6485-6490; Journal Volume: 129; Journal Issue: 20
Country of Publication:
United States
Language:
English
Subject:
08 HYDROGEN; 29 ENERGY PLANNING, POLICY AND ECONOMY; ALLOYS; CATALYSIS; CATALYSTS; DESORPTION; EFFICIENCY; FORMATES; FOSSIL FUELS; FUNCTIONALS; HYDROGEN; HYDROGEN PRODUCTION; POISONING; SCANNING TUNNELING MICROSCOPY; WATER GAS; X-RAY PHOTOELECTRON SPECTROSCOPY; Environmental Molecular Sciences Laboratory

Citation Formats

Knudsen, Jan, Nilekar, Anand U., Vang, Ronnie T., Schnadt, Joachim, Kunkes, Edward L., Dumesic, James A., Mavrikakis, Manos, and Besenbacher, Fleming. A Cu/Pt Near-Surface Alloy for Water-Gas Shift Catalysis.. United States: N. p., 2007. Web. doi:10.1021/ja0700855.
Knudsen, Jan, Nilekar, Anand U., Vang, Ronnie T., Schnadt, Joachim, Kunkes, Edward L., Dumesic, James A., Mavrikakis, Manos, & Besenbacher, Fleming. A Cu/Pt Near-Surface Alloy for Water-Gas Shift Catalysis.. United States. doi:10.1021/ja0700855.
Knudsen, Jan, Nilekar, Anand U., Vang, Ronnie T., Schnadt, Joachim, Kunkes, Edward L., Dumesic, James A., Mavrikakis, Manos, and Besenbacher, Fleming. Tue . "A Cu/Pt Near-Surface Alloy for Water-Gas Shift Catalysis.". United States. doi:10.1021/ja0700855.
@article{osti_989063,
title = {A Cu/Pt Near-Surface Alloy for Water-Gas Shift Catalysis.},
author = {Knudsen, Jan and Nilekar, Anand U. and Vang, Ronnie T. and Schnadt, Joachim and Kunkes, Edward L. and Dumesic, James A. and Mavrikakis, Manos and Besenbacher, Fleming},
abstractNote = {The research described in this product was performed in part in the Environmental Molecular Sciences Laboratory, a national scientific user facility sponsored by the Department of Energy's Office of Biological and Environmental Research and located at Pacific Northwest National Laboratory. The primary route to hydrogen production from fossil fuels involves the water-gas shift (WGS) reaction, and an improvement in the efficiency of WGS catalysts could therefore lead to a major leap forward in the realization of hydrogen economy. On the basis of a combination of high-resolution scanning tunneling microscopy, X-ray photoelectron spectroscopy, and density functional theory (DFT) calculations, we suggest the existence of a new thermodynamically stable Cu/Pt near-surface alloy (NSA). Temperature-programmed desorption and DFT reveal that this Cu/Pt NSA binds CO significantly more weakly than does Pt alone, thereby implying a considerable reduction in the potential for CO poisoning of the Cu/Pt NSA surface as compared to that of pure Pt. In addition, DFT calculations show that this Cu/Pt NSA is able to activate H2O easily, which is the rate-determining step for the WGS on several metal surfaces, and, at the same time, to bind the products of that reaction and formate intermediates rather weakly, thus avoiding possible poisoning of the catalyst surface. The Cu/Pt NSA is thus a promising candidate for an improved WGS catalyst.},
doi = {10.1021/ja0700855},
journal = {Journal of the American Chemical Society, 129(20):6485-6490},
number = 20,
volume = 129,
place = {United States},
year = {Tue May 01 00:00:00 EDT 2007},
month = {Tue May 01 00:00:00 EDT 2007}
}
  • A newly developed in situ X-ray diffraction (XRD) cell has been used to obtain information on the structure of binary Cu-Zn and ternary Cu-Zn-Al catalysts during reduction and water gas shift and methanol synthesis. A major advantage of the cell is that it also serves as an ideal plug flow catalytic reactor such that realistic catalytic and structural information can be obtained simultaneously on the same sample. The cell can be operated both at high temperatures and high pressures. Direct methanol activity tests confirmed the suitability of the cell. By use of X rays from a synchrotron source, dynamic studiesmore » on the time scale of seconds have been demonstrated. This feature was used to study the phase transformation occurring during the activation of the calcined catalysts. In the active catalyst, Cu metal is the only crystalline Cu phase observed, and the formation of this phase is seen to be closely related to the disappearance of CuO in the calcined catalyst. The XRD results provide detailed information on the nucleation and growth processes. The variation in the water gas shift activity appears to correlate with the changes in the copper surface area.« less
  • The behavior of reaction intermediates in the catalytic water-gas shift reaction (WGSR) on ZnO surfaces has been studied by means of FT-IR spectroscopy, and a reactant-promoted mechanism including intermediate-reactant interaction is proposed. On-top (terminal) hydroxyl groups on Zn ions which are formed by the first-adsorbed water molecules react with CO to produce bidentate and bridge formates. Seventy percent of them were decomposed to original CO and surface hydroxyls and only 30% of them were converted to H{sub 2} and CO{sub 2} (adsorbed) under vacuum. On the contrary, 100% of the formates were converted to the WGSR products, H{sub 2}, andmore » CO{sub 2} in coexistence with second-adsorbed water molecules. The rate of the formate decomposition was promoted by a factor of more than 10 by the presence of a second water molecule. The activation energy of the decomposition of the surface formates decreases in the presence of water; 155 kJ mol{sup {minus}1} under vacuum and 109 kJ mol{sup {minus}1} with ambient water. The rate-determining step of the decomposition is the scission of the C-H bond of the formates according to isotope effects. In the absence of ambient water vapor, adsorbed CO{sub 2} species exist as unidentate carbonate and carboxylate on ZnO surface. Steady-state rate of catalytic WGSR agree with the decomposition rates of the bidentate formate and the unidentate carbonate; the two decomposition rates are balancing during the steady-state WGSR on ZnO. Water molecules not only act as a reactant to form the formate, but also activate the bidentate formate(ad) to decompose to H{sub 2} and unidentate carbonate(ad) and promote the desorption of the carbonate as CO{sub 2}.« less
  • Alloys have become important catalysts for many chemical processes due to their superior properties over single component catalysts. These include increased reaction selectivity and greater resistance to deactivation. The reasons for their superior performance are not well understood, however. Catalytic studies, using single component metal single crystal catalysts, coupled with the use of surface science techniques, have proven useful in understanding the nature of the working catalyst. Extension of these investigations to alloy single crystal at high pressures should be useful for elucidating the role of alloying in altering catalytic behavior. In this note the authors report the surface structuremore » sensitivity of the catalytic properties of platinum-gold alloys in the conversion reaction of n-hexane and present evidence for a mixed Au-Pt site on the (111) surface for the isomerization reaction. Experiments were carried out in an ultrahigh vacuum system equipped with Auger electron spectroscopy (AES), low energy electron diffraction (LEED) optics, a quadrupole mass spectrometer, and a sample isolation cell which was connected to the reactor loop and gas chromatograph equipped with a flame ionization detector. 11 references.« less