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Title: Evaluating Thermal Corrections for Adsorption Processes at the Metal/Gas Interface

Abstract

Adsorption and desorption steps are key for active catalysts and rely on a subtle balance between enthalpic and entropic terms. Although the enthalpic term is becoming ever more accurate through density functional development, the entropic term remains underrated and its precise determination a great challenge. In this work, we have performed extensive first principles thermodynamic integration (TI) simulations for the adsorption of small (e.g., CO) to larger (e.g., phenol) molecules at metallic surfaces and compared their adsorption free energies to the values obtained by vertical, static statistical mechanics approximations to thermal corrections invoking three different approximations for the low-frequency modes. We have found an excellent agreement between the vertical corrections and the TI for minima, for both weakly bound systems (e.g. CO 2 and formic acid) and strongly chemisorbed molecules such as phenol or CO. While the treatment of the low-frequency modes has a minor impact on the agreement with TI, all vertical corrections systematically overestimate activation energies by 0.1-0.2 eV compared to TI, demonstrating a noticeable lowering of activation barriers. As an effect of this study, we suggest that the vertical corrections and in particular the standard harmonic approximation can be safely applied to chemisorption minima, while the activationmore » energies are likely to be overestimated. Hence, if a greater accuracy than ~0.2 eV is required for activation free energies, we recommend to use thermodynamic integration, which for small to medium-sized molecules in gas phase is accessible with a reasonable computational effort, but requires a dense sampling in the transition state region.« less

Authors:
ORCiD logo [1]; ORCiD logo [1]; ORCiD logo [2]; ORCiD logo [3]; ORCiD logo [1]
  1. Claude Bernard Univ. Lyon 1 (France)
  2. Univ. of Burgundy-Franche-Comté (France)
  3. Univ. of California, Los Angeles, CA (United States)
Publication Date:
Research Org.:
Harvard Univ., Cambridge, MA (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22); French National Research Agency
OSTI Identifier:
1595613
Grant/Contract Number:  
SC0012573
Resource Type:
Accepted Manuscript
Journal Name:
Journal of Physical Chemistry. C
Additional Journal Information:
Journal Volume: 123; Journal Issue: 47; Journal ID: ISSN 1932-7447
Publisher:
American Chemical Society
Country of Publication:
United States
Language:
English

Citation Formats

Réocreux, Romain, Michel, Carine, Fleurat-Lessard, Paul, Sautet, Philippe, and Steinmann, Stephan N. Evaluating Thermal Corrections for Adsorption Processes at the Metal/Gas Interface. United States: N. p., 2019. Web. doi:10.1021/acs.jpcc.9b09863.
Réocreux, Romain, Michel, Carine, Fleurat-Lessard, Paul, Sautet, Philippe, & Steinmann, Stephan N. Evaluating Thermal Corrections for Adsorption Processes at the Metal/Gas Interface. United States. doi:10.1021/acs.jpcc.9b09863.
Réocreux, Romain, Michel, Carine, Fleurat-Lessard, Paul, Sautet, Philippe, and Steinmann, Stephan N. Wed . "Evaluating Thermal Corrections for Adsorption Processes at the Metal/Gas Interface". United States. doi:10.1021/acs.jpcc.9b09863.
@article{osti_1595613,
title = {Evaluating Thermal Corrections for Adsorption Processes at the Metal/Gas Interface},
author = {Réocreux, Romain and Michel, Carine and Fleurat-Lessard, Paul and Sautet, Philippe and Steinmann, Stephan N.},
abstractNote = {Adsorption and desorption steps are key for active catalysts and rely on a subtle balance between enthalpic and entropic terms. Although the enthalpic term is becoming ever more accurate through density functional development, the entropic term remains underrated and its precise determination a great challenge. In this work, we have performed extensive first principles thermodynamic integration (TI) simulations for the adsorption of small (e.g., CO) to larger (e.g., phenol) molecules at metallic surfaces and compared their adsorption free energies to the values obtained by vertical, static statistical mechanics approximations to thermal corrections invoking three different approximations for the low-frequency modes. We have found an excellent agreement between the vertical corrections and the TI for minima, for both weakly bound systems (e.g. CO2 and formic acid) and strongly chemisorbed molecules such as phenol or CO. While the treatment of the low-frequency modes has a minor impact on the agreement with TI, all vertical corrections systematically overestimate activation energies by 0.1-0.2 eV compared to TI, demonstrating a noticeable lowering of activation barriers. As an effect of this study, we suggest that the vertical corrections and in particular the standard harmonic approximation can be safely applied to chemisorption minima, while the activation energies are likely to be overestimated. Hence, if a greater accuracy than ~0.2 eV is required for activation free energies, we recommend to use thermodynamic integration, which for small to medium-sized molecules in gas phase is accessible with a reasonable computational effort, but requires a dense sampling in the transition state region.},
doi = {10.1021/acs.jpcc.9b09863},
journal = {Journal of Physical Chemistry. C},
number = 47,
volume = 123,
place = {United States},
year = {2019},
month = {10}
}

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This content will become publicly available on October 30, 2020
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