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Title: Preferential CO Oxidation in Hydrogen: Reactivity of Core-Shell Nanoparticles

Abstract

We report on the first-principles-guided design, synthesis, and characterization of core-shell nanoparticle (NP) catalysts made of a transition metal core (M ) Ru, Rh, Ir, Pd, or Au) covered with a ~1-2 monolayer thick shell of Pt atoms (i.e., a M@Pt core-shell NP). An array of experimental techniques, including X-ray diffraction, Fourier transform infrared spectroscopy, high resolution transmission electron microscopy, and temperature-programmed reaction, are employed to establish the composition of the synthesized NPs. Subsequent studies of these NPs’ catalytic properties for preferential CO oxidation in hydrogen-rich environments (PROX), combined with Density Functional Theory (DFT)-based mechanistic studies, elucidate important trends and provide fundamental understanding of the reactivity of Pt shells as a function of the core metal. Both the PROX activity and selectivity of several of these M@Pt core-shell NPs are significantly improved compared to monometallic and bulk nonsegregated bimetallic nanoalloys. Among the systems studied, Ru@Pt core-shell NPs exhibit the highest PROX activity, where the CO oxidation is complete by 30 °C (1000 ppm CO in H 2). Therefore, despite their reduced Pt content, M@Pt core-shell NPs afford the design of more active PROX catalysts. DFT studies suggest that the relative differences in the catalytic activities for the various core-shell NPsmore » originate from a combination of (i) the relative availability of CO-free Pt surface sites on the M@Pt NPs, which are necessary for O 2 activation, and (ii) a hydrogen-mediated low-temperature CO oxidation process that is clearly distinct from the traditional bifunctional CO oxidation mechanism.« less

Authors:
; ; ;
Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Oak Ridge Leadership Computing Facility (OLCF); Pacific Northwest National Laboratory (PNNL), Richland, WA (US), Environmental Molecular Sciences Laboratory (EMSL)
Sponsoring Org.:
USDOE Office of Science (SC)
OSTI Identifier:
1001487
DOE Contract Number:  
AC05-76RL01830
Resource Type:
Journal Article
Journal Name:
Journal of the American Chemical Society
Additional Journal Information:
Journal Volume: 132; Journal Issue: 21; Journal ID: ISSN 0002-7863
Publisher:
American Chemical Society (ACS)
Country of Publication:
United States
Language:
English
Subject:
08 HYDROGEN; ATOMS; AVAILABILITY; CATALYSTS; DESIGN; FUNCTIONALS; HYDROGEN; OXIDATION; RESOLUTION; SPECTROSCOPY; SYNTHESIS; TRANSITION ELEMENTS; TRANSMISSION ELECTRON MICROSCOPY; X-RAY DIFFRACTION; Environmental Molecular Sciences Laboratory

Citation Formats

Nilekar, Anand U, Alayoglu, Selim, Eichhorn, Bryan W, and Mavrikakis, Manos. Preferential CO Oxidation in Hydrogen: Reactivity of Core-Shell Nanoparticles. United States: N. p., 2010. Web. doi:10.1021/ja101108w.
Nilekar, Anand U, Alayoglu, Selim, Eichhorn, Bryan W, & Mavrikakis, Manos. Preferential CO Oxidation in Hydrogen: Reactivity of Core-Shell Nanoparticles. United States. doi:10.1021/ja101108w.
Nilekar, Anand U, Alayoglu, Selim, Eichhorn, Bryan W, and Mavrikakis, Manos. Wed . "Preferential CO Oxidation in Hydrogen: Reactivity of Core-Shell Nanoparticles". United States. doi:10.1021/ja101108w.
@article{osti_1001487,
title = {Preferential CO Oxidation in Hydrogen: Reactivity of Core-Shell Nanoparticles},
author = {Nilekar, Anand U and Alayoglu, Selim and Eichhorn, Bryan W and Mavrikakis, Manos},
abstractNote = {We report on the first-principles-guided design, synthesis, and characterization of core-shell nanoparticle (NP) catalysts made of a transition metal core (M ) Ru, Rh, Ir, Pd, or Au) covered with a ~1-2 monolayer thick shell of Pt atoms (i.e., a M@Pt core-shell NP). An array of experimental techniques, including X-ray diffraction, Fourier transform infrared spectroscopy, high resolution transmission electron microscopy, and temperature-programmed reaction, are employed to establish the composition of the synthesized NPs. Subsequent studies of these NPs’ catalytic properties for preferential CO oxidation in hydrogen-rich environments (PROX), combined with Density Functional Theory (DFT)-based mechanistic studies, elucidate important trends and provide fundamental understanding of the reactivity of Pt shells as a function of the core metal. Both the PROX activity and selectivity of several of these M@Pt core-shell NPs are significantly improved compared to monometallic and bulk nonsegregated bimetallic nanoalloys. Among the systems studied, Ru@Pt core-shell NPs exhibit the highest PROX activity, where the CO oxidation is complete by 30 °C (1000 ppm CO in H2). Therefore, despite their reduced Pt content, M@Pt core-shell NPs afford the design of more active PROX catalysts. DFT studies suggest that the relative differences in the catalytic activities for the various core-shell NPs originate from a combination of (i) the relative availability of CO-free Pt surface sites on the M@Pt NPs, which are necessary for O2 activation, and (ii) a hydrogen-mediated low-temperature CO oxidation process that is clearly distinct from the traditional bifunctional CO oxidation mechanism.},
doi = {10.1021/ja101108w},
journal = {Journal of the American Chemical Society},
issn = {0002-7863},
number = 21,
volume = 132,
place = {United States},
year = {2010},
month = {6}
}