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Understanding Reaction Networks through Controlled Approach to Equilibrium Experiments Using Transient Methods

Wang, Yixiao and Qian, Jin and Fang, Zongtang and Kunz, M. Ross and Yablonsky, Gregory and Fortunelli, Alessandro and Goddard, William A., III and Fushimi, Rebecca R. (2021) Understanding Reaction Networks through Controlled Approach to Equilibrium Experiments Using Transient Methods. Journal of the American Chemical Society, 143 (29). pp. 10998-11006. ISSN 1520-5126. doi:10.1021/jacs.1c03158.

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We report a combined experimental/theoretical approach to studying heterogeneous gas/solid catalytic processes using low-pressure pulse response experiments achieving a controlled approach to equilibrium that combined with quantum mechanics (QM)-based computational analysis provides information needed to reconstruct the role of the different surface reaction steps. We demonstrate this approach using model catalysts for ammonia synthesis/decomposition. Polycrystalline iron and cobalt are studied via low-pressure TAP (temporal analysis of products) pulse response, with the results interpreted through reaction free energies calculated using QM on Fe-BCC(110), Fe-BCC(111), and Co-FCC(111) facets. In TAP experiments, simultaneous pulsing of ammonia and deuterium creates a condition where the participation of reactants and products can be distinguished in both forward and reverse reaction steps. This establishes a balance between competitive reactions for D* surface species that is used to observe the influence of steps leading to nitrogen formation as the nitrogen product remains far from equilibrium. The approach to equilibrium is further controlled by introducing delay timing between NH₃ and D₂ which allows time for surface reactions to evolve before being driven in the reverse direction from the gas phase. The resulting isotopic product distributions for NH₂D, NHD₂, and HD at different temperatures and delay times and NH₃/D₂ pulsing order reveal the role of the N₂ formation barrier in controlling the surface concentration of NH_x* species, as well as providing information on the surface lifetimes of key reaction intermediates. Conclusions derived for monometallic materials are used to interpret experimental results on a more complex and active CoFe bimetallic catalyst.

Item Type:Article
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URLURL TypeDescription Information
Qian, Jin0000-0002-0162-0477
Fortunelli, Alessandro0000-0001-5337-4450
Goddard, William A., III0000-0003-0097-5716
Additional Information:© 2021 American Chemical Society. Received: April 1, 2021; Published: July 19, 2021. This work was supported by U.S. Department of Energy (USDOE), Office of Energy Efficiency and Renewable Energy (EERE), Advanced Manufacturing Office Next Generation R&D Projects under Contract No. DE-AC07-05ID14517. The authors express gratitude to Dickson Ozokwelu for his support and dedicate this manuscript to his memory. In addition, A.F. and W.A.G. received support from NSF (CBET-1805022 and CBET-2005250). The authors declare no competing financial interest.
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Department of Energy (DOE)DE-AC07-05ID14517
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Issue or Number:29
Record Number:CaltechAUTHORS:20210730-165147361
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Official Citation:Understanding Reaction Networks through Controlled Approach to Equilibrium Experiments Using Transient Methods. Yixiao Wang, Jin Qian, Zongtang Fang, M. Ross Kunz, Gregory Yablonsky, Alessandro Fortunelli, William A. Goddard III, and Rebecca R. Fushimi. Journal of the American Chemical Society 2021 143 (29), 10998-11006; DOI: 10.1021/jacs.1c03158
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:110099
Deposited By: Donna Wrublewski
Deposited On:30 Jul 2021 17:39
Last Modified:02 Aug 2021 21:39

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