Title: Nature of Reactive Hydrogen for Ammonia Synthesis over a Ru/C12A7 Electride Catalyst

Abstract

Recently, there have been renewed interests in exploring new catalysts for ammonia synthesis under mild conditions. Electride-based catalysts are among the emerging ones. Ruthenium particles supported on an electride composed of a mixture of calcium and aluminum oxides (C12A7) have attracted great attention for ammonia synthesis due to their facile ability in activating N2 under ambient pressure. However, the exact nature of the reactive hydrogen species and the role of electride support still remain elusive for this catalytic system. Here, we report for the first time that the surface-adsorbed hydrogen, rather than the hydride encaged in the C12A7 electride, plays a major role in ammonia synthesis over the Ru/C12A7 electride catalyst with the aid of in situ neutron scattering techniques. Combining in situ neutron diffraction, inelastic neutron spectroscopy, density functional theory (DFT) calculation, and temperature-programmed reactions, the results provide direct evidence for not only the presence of encaged hydrides during ammonia synthesis but also the strong thermal and chemical stability of the hydride species in the Ru/C12A7 electride. Steady state isotopic transient kinetic analysis (SSITKA) of ammonia synthesis showed that the coverage of reactive intermediates increased significantly when the Ru particles were promoted by the electride form (coverage up tomore » 84%) of the C12A7 support rather than the oxide form (coverage up to 15%). Such a drastic change in the intermediate coverage on the Ru surface is attributed to the positive role of electride support where the H2 poisoning effect is absent during ammonia synthesis over Ru. The finding of this work has significant implications for understanding catalysis by electride-based materials for ammonia synthesis and hydrogenation reactions in general.« less

Authors:

Kammert, James ^[1]; Moon, Jisue ^[2]; Cheng, Yongqiang  ^[3];

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• Search DOE PAGES for ORCID "0000-0002-3263-4812"

Daemen, Luke L. ^[3]; Irle, Stephan  ^[1];

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• Search DOE PAGES for ORCID "0000-0003-4995-4991"

Fung, Victor  ^[4];

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Liu, Jue  ^[3];

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Page, Katharine  ^[3];

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• Search DOE PAGES for ORCID "0000-0002-9071-3383"

Ma, Xiaohan ^[5]; Phaneuf, Vincent ^[6]; Tong, Jianhua  ^[6];

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Ramirez Cuesta, Anibal  ^[3];

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Wu, Zili  ^[2]

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• Search DOE PAGES for ORCID "0000-0002-4468-3240"

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+ Show Author Affiliations

1. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Chemical Sciences Division
2. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Chemical Sciences Division and Center for Nanophase Materials Sciences (CNMS)
3. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Neutron Scattering Division
4. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Center for Nanophase Materials Sciences (CNMS)
5. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Center for Nanophase Materials Sciences (CNMS); Clemson Univ., SC (United States). Dept. of Materials Science and Engineering
6. Clemson Univ., SC (United States). Dept. of Materials Science and Engineering

Publication Date:

Sat Apr 04 00:00:00 EDT 2020

Research Org.:

Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States). Spallation Neutron Source (SNS)

Sponsoring Org.:

USDOE Laboratory Directed Research and Development (LDRD) Program; USDOE Office of Science (SC)

OSTI Identifier:

1649278

Grant/Contract Number:  

AC05-00OR22725; AC02-05CH11231

Resource Type:

Accepted Manuscript

Journal Name:

Journal of the American Chemical Society

Additional Journal Information:

Journal Volume: 142; Journal Issue: 16; Journal ID: ISSN 0002-7863

Publisher:

American Chemical Society (ACS)

Country of Publication:

United States

Language:

English

Subject:

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; anions; ammonia; mixtures; catalysts; neutron diffraction