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Discovery of Dramatically Improved Ammonia Synthesis Catalysts through Hierarchical High-Throughput Catalyst Screening of the Fe(211) Surface

Fuller, Jon and Fortunelli, Alessandro and Goddard, William A., III and An, Qi (2020) Discovery of Dramatically Improved Ammonia Synthesis Catalysts through Hierarchical High-Throughput Catalyst Screening of the Fe(211) Surface. Chemistry of Materials, 32 (23). pp. 9914-9924. ISSN 0897-4756. doi:10.1021/acs.chemmater.0c02701.

[img] PDF (Preferred positions of elements in the first and second layer for Fe-bcc(211)R; lowest-energy state for doping elements in Fe-bcc(211)R; convergence with respect to kMC steps for Co-doped and pure Fe-bcc(211)R surfaces; preferred positions of HHTCS...) - Supplemental Material
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[img] MS Excel (Raw DFT data for HHTCS) - Supplemental Material
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[img] MS Excel (Raw data for the reaction energy path of the HB process on the Co-doped Fe-bcc(211)R surface) - Supplemental Material
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In order to improve efficiency of ammonia synthesis using the Haber–Bosch (HB) process with Fe-based catalysts, we employed quantum mechanics (QM)-based hierarchical high-throughput catalyst screening (HHTCS) of 49 possible metal dopants. Here, we consider the Fe(211) surface (one of the two most active iron catalyst facets) to identify dopants that dramatically increase the turnover frequency (TOF) for HB synthesis. We found that under HB conditions, this surface reconstructs to form the Fe(211)R missing-row surface. Focusing on dopants with a strong preference for the subsurface site, we found that Co is the most promising candidate among the 49. We then examined the full reaction pathway on this Co-doped Fe(211)R surface, considering all 19 important 2 × 2 configurations and calculated the free-energy barriers (ΔG∫) for all 12 important reaction steps. At 673 K and 20 atm, we find a decrease, δ(ΔG∫) = −0.19 eV, in the overall reaction free-energy barrier for the Co-doped case. We then carried out kinetic Monte Carlo simulations for 60–120 min using 100 replicas with the full reaction path using rates from QM free-energy reaction barriers to predict that the TOF for the Co-doped surface increases by a factor of 2.8 with respect to the undoped Fe(211)R surface. Thus, the Co-doped Fe(211)R system could lower the extreme HB pressure of 200 atm to ∼40 atm at 773 K while maintaining the same TOF as that of undoped Fe(211)R. We conclude that Co dopants in the Fe catalyst could significantly improve the catalytic efficiency of ammonia synthesis under industrial conditions. This excellent performance of the Co-doped system is explained in terms of a surface spin analysis on the N₂-bonded configurations that show how Co dopants shift the N₂ surface-binding mode. This demonstrates that metal surface spins can be used as quantitative descriptors to understand reaction energetics. This study demonstrates that the HHTCS kinetic analysis of the free-energy reaction path in terms of essential configurations can enable discovery of the salient barriers to overcome and best dopant candidates for further improvements.

Item Type:Article
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URLURL TypeDescription
Fuller, Jon0000-0003-1233-7842
Fortunelli, Alessandro0000-0001-5337-4450
Goddard, William A., III0000-0003-0097-5716
An, Qi0000-0003-4838-6232
Additional Information:© 2020 American Chemical Society. Received: June 26, 2020; Revised: October 28, 2020; Published: November 17, 2020. J.F. was supported by DOE-NEUP under grant no. DE-NE0008889. A.F. gratefully acknowledges the contribution of the International Research Network IRN on Nanoalloys (CNRS). A.F. and WAG received support from NSF (CBET-1805022). The authors declare no competing financial interest.
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Department of Energy (DOE)DE-NE0008889
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Issue or Number:23
Record Number:CaltechAUTHORS:20201117-111718419
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Official Citation:Discovery of Dramatically Improved Ammonia Synthesis Catalysts through Hierarchical High-Throughput Catalyst Screening of the Fe(211) Surface. Jon Fuller, Alessandro Fortunelli, William A. Goddard, and Qi An. Chemistry of Materials 2020 32 (23), 9914-9924; DOI: 10.1021/acs.chemmater.0c02701
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:106703
Deposited By: Tony Diaz
Deposited On:17 Nov 2020 19:25
Last Modified:16 Nov 2021 18:56

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