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Title: Peptide-Directed PdAu Nanoscale Surface Segregation: Toward Controlled Bimetallic Architecture for Catalytic Materials

Abstract

Bimetallic nanoparticles are of immense scientific and technological interest given the synergistic properties observed when mixing two different metallic species at the nanoscale. This is particularly prevalent in catalysis, where bimetallic nanoparticles often exhibit improved catalytic activity and durability over their monometallic counterparts. Yet despite intense research efforts, little is understood regarding how to optimize bimetallic surface composition and structure synthetically using rational design principles. Recently, it has been demonstrated that peptide-enabled routes for nanoparticle synthesis result in materials with sequence-dependent catalytic properties, providing an opportunity for rational design through sequence manipulation. In this study, bimetallic PdAu nanoparticles are synthesized with a small set of peptides containing known Pd and Au binding motifs. The resulting nanoparticles were extensively characterized using high-resolution scanning transmission electron microscopy, X-ray absorption spectroscopy and high-energy X-ray diffraction coupled to atomic pair distribution function analysis. Structural information obtained from synchrotron radiation methods were then used to generate model nanoparticle configurations using reverse Monte Carlo simulations, which illustrate sequence-dependence in both surface structure and surface composition. Replica exchange solute tempering molecular dynamic simulations were also used to predict the modes of peptide binding on monometallic surfaces, indicating that different sequences bind to the metal interfaces via differentmore » mechanisms. As a testbed reaction, electrocatalytic methanol oxidation experiments were performed, wherein differences in catalytic activity are clearly observed in materials with identical bimetallic composition. Finally, taken together, this study indicates that peptides could be used to arrive at bimetallic surfaces with enhanced catalytic properties, which could be leveraged for rational bimetallic nanoparticle design using peptide-enabled approaches.« less

Authors:
 [1];  [2];  [1];  [3];  [4];  [4];  [5];  [5];  [4];  [3];  [2]
  1. National Inst. of Standards and Technology (NIST), Boulder, CO (United States)
  2. Univ. of Notre Dame, IN (United States). Dept. of Physics
  3. Deakin Univ., Geelong, Victoria (Australia). Inst. for Frontier Materials
  4. Argonne National Lab. (ANL), Argonne, IL (United States). X-ray Sciences Division
  5. Univ. of Massachusetts, Amherst, MA (United States). Dept. of Polymer Science and Engineering
Publication Date:
Research Org.:
Argonne National Lab. (ANL), Argonne, IL (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22); US Air Force Office of Scientific Research (AFOSR); Australian Government; National Science Foundation (NSF)
OSTI Identifier:
1368096
Grant/Contract Number:
AC02-06CH11357; FA9550-12-620 1-0226
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
ACS Nano
Additional Journal Information:
Journal Volume: 10; Journal Issue: 9; Journal ID: ISSN 1936-0851
Publisher:
American Chemical Society (ACS)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; atomic pair distribution function analysis; bimetallic nanoparticles; core-shell nanoparticles; electrocatalysis; peptide-enabled nanoparticles; x-ray absorption spectroscopy; x-ray diffraction

Citation Formats

Bedford, Nicholas M., Showalter, Allison R., Woehl, Taylor J., Hughes, Zak E., Lee, Sungsik, Reinhart, Benjamin, Ertem, S. Piril, Coughlin, E. Bryan, Ren, Yang, Walsh, Tiffany R., and Bunker, Bruce A.. Peptide-Directed PdAu Nanoscale Surface Segregation: Toward Controlled Bimetallic Architecture for Catalytic Materials. United States: N. p., 2016. Web. doi:10.1021/acsnano.6b03963.
Bedford, Nicholas M., Showalter, Allison R., Woehl, Taylor J., Hughes, Zak E., Lee, Sungsik, Reinhart, Benjamin, Ertem, S. Piril, Coughlin, E. Bryan, Ren, Yang, Walsh, Tiffany R., & Bunker, Bruce A.. Peptide-Directed PdAu Nanoscale Surface Segregation: Toward Controlled Bimetallic Architecture for Catalytic Materials. United States. doi:10.1021/acsnano.6b03963.
Bedford, Nicholas M., Showalter, Allison R., Woehl, Taylor J., Hughes, Zak E., Lee, Sungsik, Reinhart, Benjamin, Ertem, S. Piril, Coughlin, E. Bryan, Ren, Yang, Walsh, Tiffany R., and Bunker, Bruce A.. 2016. "Peptide-Directed PdAu Nanoscale Surface Segregation: Toward Controlled Bimetallic Architecture for Catalytic Materials". United States. doi:10.1021/acsnano.6b03963. https://www.osti.gov/servlets/purl/1368096.
@article{osti_1368096,
title = {Peptide-Directed PdAu Nanoscale Surface Segregation: Toward Controlled Bimetallic Architecture for Catalytic Materials},
author = {Bedford, Nicholas M. and Showalter, Allison R. and Woehl, Taylor J. and Hughes, Zak E. and Lee, Sungsik and Reinhart, Benjamin and Ertem, S. Piril and Coughlin, E. Bryan and Ren, Yang and Walsh, Tiffany R. and Bunker, Bruce A.},
abstractNote = {Bimetallic nanoparticles are of immense scientific and technological interest given the synergistic properties observed when mixing two different metallic species at the nanoscale. This is particularly prevalent in catalysis, where bimetallic nanoparticles often exhibit improved catalytic activity and durability over their monometallic counterparts. Yet despite intense research efforts, little is understood regarding how to optimize bimetallic surface composition and structure synthetically using rational design principles. Recently, it has been demonstrated that peptide-enabled routes for nanoparticle synthesis result in materials with sequence-dependent catalytic properties, providing an opportunity for rational design through sequence manipulation. In this study, bimetallic PdAu nanoparticles are synthesized with a small set of peptides containing known Pd and Au binding motifs. The resulting nanoparticles were extensively characterized using high-resolution scanning transmission electron microscopy, X-ray absorption spectroscopy and high-energy X-ray diffraction coupled to atomic pair distribution function analysis. Structural information obtained from synchrotron radiation methods were then used to generate model nanoparticle configurations using reverse Monte Carlo simulations, which illustrate sequence-dependence in both surface structure and surface composition. Replica exchange solute tempering molecular dynamic simulations were also used to predict the modes of peptide binding on monometallic surfaces, indicating that different sequences bind to the metal interfaces via different mechanisms. As a testbed reaction, electrocatalytic methanol oxidation experiments were performed, wherein differences in catalytic activity are clearly observed in materials with identical bimetallic composition. Finally, taken together, this study indicates that peptides could be used to arrive at bimetallic surfaces with enhanced catalytic properties, which could be leveraged for rational bimetallic nanoparticle design using peptide-enabled approaches.},
doi = {10.1021/acsnano.6b03963},
journal = {ACS Nano},
number = 9,
volume = 10,
place = {United States},
year = 2016,
month = 9
}

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  • The surface composition and structure are of vital importance for heterogeneous catalysts, especially for bimetallic catalysts, which often vary as a function of reaction conditions (known as surface segregation). The preparation of bimetallic catalysts with controlled metal surface composition and structure is very challenging. In this study, we synthesize a series of Ni/Pt bimetallic catalysts with controlled metal surface composition and structure using a method derived from surface organometallic chemistry. Moreover, the evolution of the surface composition and structure of the obtained bimetallic catalysts under simulated reaction conditions is investigated by various techniques, which include CO-probe IR spectroscopy, high-angle annularmore » dark-field scanning transmission electron microscopy, energy-dispersive X-ray spectroscopy, extended X-ray absorption fine structure analysis, X-ray absorption near-edge structure analysis, XRD, and X-ray photoelectron spectroscopy. It is demonstrated that the structure of the bimetallic catalyst is evolved from Pt monolayer island-modified Ni nanoparticles to core–shell bimetallic nanoparticles composed of a Ni-rich core and a Ni/Pt alloy shell upon thermal treatment. The catalysts are active for the dry reforming of methane, and their catalytic activities, stabilities, and carbon formation vary with their surface composition and structure.« less
  • Surface composition and structure are of vital importance for heterogeneous catalysts, especially for bimetallic catalysts, which often vary as a function of reaction conditions (known as surface segregation). The preparation of bimetallic catalysts with controlled metal surface composition and structure is very challenging. In this study, we synthesize a series of Ni/Pt bimetallic catalysts with controlled metal surface composition and structure using a method derived from surface organometallic chemistry. The evolution of the surface composition and structure of the obtained bimetallic catalysts under simulated reaction conditions is investigated by various techniques, which include CO-probe IR spectroscopy, high-angle annular dark-field scanningmore » transmission electron microscopy, energy-dispersive X-ray spectroscopy, extended X-ray absorption fine structure analysis, X-ray absorption near-edge structure analysis, XRD, and X-ray photoelectron spectroscopy. It is demonstrated that the structure of the bimetallic catalyst is evolved from Pt monolayer island-modified Ni nanoparticles to core–shell bimetallic nanoparticles composed of a Ni-rich core and a Ni/Pt alloy shell upon thermal treatment. As a result, these catalysts are active for the dry reforming of methane, and their catalytic activities, stabilities, and carbon formation vary with their surface composition and structure.« less
  • Here we present evidence for an oxidation-driven structural conversion of quasi-alloy PdAu dendrimer-encapsulated nanoparticles (DENs) to a Au-core/Pd-shell configuration. The initial quasialloy was prepared by co-complexation of PdCl42- and AuCl4- within a sixth-generation, poly(amidoamine) dendrimer template followed by chemical reduction. Exposure to air resulted in selective reoxidation of the Pd atoms and subsequent re-reduction led to deposition of a Pd-rich shell on the surface of the remaining Au core. The core/shell nanoparticles were extracted as monolayer-protected clusters (MPCs) from within the dendrimer templates using dodecanethiol. The resulting materials were characterized by UV-vis spectroscopy, transmission electron microscopy, and extended X-ray absorptionmore » fine structure (EXAFS) spectroscopy.« less
  • A combination of two synchrotron X-ray techniques, X-ray absorption spectroscopy (XAS), and pair distribution function analysis (PDF) with complementary Fourier transform infrared (FTIR) spectroscopy measurement, was used to characterize the composition distributions of PdAu and PtCu bimetallic particles after treatment in H{sub 2} or CO and in the presence of these gases. This is the first reported application of PDF to the study of supported bimetallic nanoparticles. We found that XAS was informative in determining the component distribution of an initial sample, but PDF was better suited to following changes in the distribution upon changing the gas environment. Thus, themore » surface of a PtCu bimetallic particle of about 2.5 nm after treatment in H{sub 2} was found to be enriched in Cu, while the core was bimetallic. There was no evidence of a component-segregated core?shell structure. Treatment in CO caused enrichment of Pt to the surface layer, with a concomitant migration of Cu to the core. The average particle size remained the same. For the PdAu bimetallic particles, the surface and core compositions were similar after H{sub 2} treatment, and Pd was enriched in the surface after CO treatment. The X-ray results compared favorably to infrared spectroscopy results. The results demonstrated that the two X-ray techniques in combination can generate new information not available with either technique alone or other techniques, about the elemental distribution of bimetallic particles under conditions relevant to catalysis. They could provide new insight into structure-function relationships and time-on-stream behavior of bimetallic catalysts.« less
  • PdAu dendrimer-encapsulated nanoparticles (DENs) were prepared via sequential reduction of the component metals. When Au is reduced onto 55-atom, preformed Pd DEN cores, analysis by UV-vis spectroscopy, electron microscopy, and extended X-ray absorption fine structure (EXAFS) spectroscopy leads to a model consistent with inversion of the two metals. That is, Au migrates into the core and Pd resides on the surface. However, when Pd is reduced onto a 55-atom Au core, the expected Au core-Pd shell structure results. In this latter case, the EXAFS analysis suggests partial oxidation of the relatively thick Pd shell. When the DENs are extracted frommore » their protective dendrimer stabilizers by alkylthiols, the resulting monolayer-protected clusters retain their original Au core-Pd shell structures. The structural analysis is consistent with a study of nanoparticle-catalyzed conversion of resazurin to resorufin. The key conclusion from this work is that correlation of structure to catalytic function for very small, bimetallic nanoparticles requires detailed information about atomic configuration.« less