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Title: Kinetic Isolation between Turnovers on Au 18 Nanoclusters: Formic Acid Decomposition One Molecule at a Time

Abstract

Formic acid (HCOOH or FA) is a clean, safe, and renewable hydrogen storage material. Although Au catalysts decompose vapor-phase FA with high activity and selectivity toward hydrogen, the active site and reaction mechanism remain unclear. Here, we show that the subnanometric Au18 cluster (0.8 nm in diameter) is likely the active species for FA decomposition. We performed coverage self-consistent, density functional theory-based kinetic Monte Carlo simulations of FA decomposition on gas-phase Au18 clusters, predicting 100% selectivity toward hydrogen and turnover frequencies close to experimentally determined values. The active site is made up of a triangular ensemble of three atoms each possessing a coordination number of 5. Although there are two active site ensembles on the Au18 cluster, their occupations are strongly correlated because of strong, stabilizing interactions between pairs of open-shell adsorbates mediated by the superatomic nature of the cluster. Because the occupation of the active sites blocks the dissociation of additional HCOOH molecules, there is kinetic isolation between turnovers: only one HCOOH molecule can dissociate on the cluster at a time. This explains the extraordinary, experimentally observed selectivity of Au catalysts toward HD during decomposition of HCOOD and DCOOH. Our work offers nanoscale insights into the reaction mechanisms ofmore » FA decomposition over Au. This represents a rare example of heterogeneous catalysis by a cluster that catalyzes reactants one molecule at a time. Our work on Au18 thus sheds light on how the unique electronic properties of subnanometric clusters can be used to design quasi-molecular catalysts with high activity and selectivity.« less

Authors:
 [1]; ORCiD logo [2]; ORCiD logo [1]
  1. Department of Chemical and Biological Engineering, University of Wisconsin—Madison, Madison, Wisconsin 53706, United States
  2. Thomas Young Centre and Department of Chemical Engineering, University College London, Roberts Building, Torrington Place, London WC1E 7JE, United Kingdom
Publication Date:
Research Org.:
University of Wisconsin - Madison
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22); USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22). Chemical Sciences, Geosciences & Biosciences Division
OSTI Identifier:
1569465
Grant/Contract Number:  
FG02-05ER15731; AC02-05CH11231; AC02-06CH11357
Resource Type:
Accepted Manuscript
Journal Name:
ACS Catalysis
Additional Journal Information:
Journal Volume: 9; Journal Issue: 10; Journal ID: ISSN 2155-5435
Country of Publication:
United States
Language:
English

Citation Formats

Chen, Benjamin W. J., Stamatakis, Michail, and Mavrikakis, Manos. Kinetic Isolation between Turnovers on Au 18 Nanoclusters: Formic Acid Decomposition One Molecule at a Time. United States: N. p., 2019. Web. doi:10.1021/acscatal.9b02167.
Chen, Benjamin W. J., Stamatakis, Michail, & Mavrikakis, Manos. Kinetic Isolation between Turnovers on Au 18 Nanoclusters: Formic Acid Decomposition One Molecule at a Time. United States. doi:10.1021/acscatal.9b02167.
Chen, Benjamin W. J., Stamatakis, Michail, and Mavrikakis, Manos. Wed . "Kinetic Isolation between Turnovers on Au 18 Nanoclusters: Formic Acid Decomposition One Molecule at a Time". United States. doi:10.1021/acscatal.9b02167.
@article{osti_1569465,
title = {Kinetic Isolation between Turnovers on Au 18 Nanoclusters: Formic Acid Decomposition One Molecule at a Time},
author = {Chen, Benjamin W. J. and Stamatakis, Michail and Mavrikakis, Manos},
abstractNote = {Formic acid (HCOOH or FA) is a clean, safe, and renewable hydrogen storage material. Although Au catalysts decompose vapor-phase FA with high activity and selectivity toward hydrogen, the active site and reaction mechanism remain unclear. Here, we show that the subnanometric Au18 cluster (0.8 nm in diameter) is likely the active species for FA decomposition. We performed coverage self-consistent, density functional theory-based kinetic Monte Carlo simulations of FA decomposition on gas-phase Au18 clusters, predicting 100% selectivity toward hydrogen and turnover frequencies close to experimentally determined values. The active site is made up of a triangular ensemble of three atoms each possessing a coordination number of 5. Although there are two active site ensembles on the Au18 cluster, their occupations are strongly correlated because of strong, stabilizing interactions between pairs of open-shell adsorbates mediated by the superatomic nature of the cluster. Because the occupation of the active sites blocks the dissociation of additional HCOOH molecules, there is kinetic isolation between turnovers: only one HCOOH molecule can dissociate on the cluster at a time. This explains the extraordinary, experimentally observed selectivity of Au catalysts toward HD during decomposition of HCOOD and DCOOH. Our work offers nanoscale insights into the reaction mechanisms of FA decomposition over Au. This represents a rare example of heterogeneous catalysis by a cluster that catalyzes reactants one molecule at a time. Our work on Au18 thus sheds light on how the unique electronic properties of subnanometric clusters can be used to design quasi-molecular catalysts with high activity and selectivity.},
doi = {10.1021/acscatal.9b02167},
journal = {ACS Catalysis},
number = 10,
volume = 9,
place = {United States},
year = {2019},
month = {9}
}

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This content will become publicly available on September 4, 2020
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