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Reaction mechanism and kinetics for ammonia synthesis on the Fe(211) reconstructed surface

Fuller, Jon and Fortunelli, Alessandro and Goddard, William A., III and An, Qi (2019) Reaction mechanism and kinetics for ammonia synthesis on the Fe(211) reconstructed surface. Physical Chemistry Chemical Physics, 21 (21). pp. 11444-11454. ISSN 1463-9076. https://resolver.caltech.edu/CaltechAUTHORS:20190521-110908971

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Abstract

To provide guidelines to accelerate the Haber–Bosch (HB) process for synthesis of ammonia from hydrogen and nitrogen, we used Quantum Mechanics (QM) to determine the reaction mechanism and free energy reaction barriers under experimental reaction conditions (400 °C and 20 atm) for all 10 important surface reactions on the Fe(211) reconstructed (Fe(211)R) surface. These conditions were then used in full kMC modeling for 30 minutes to attain steady state. We find that the stable surface under Haber–Bosch conditions is the missing row 2 × 1 reconstructed surface (211)R and that the Turn Over Frequency (TOF) is 18.7 s^(−1) per 2 × 2 surface site for 1.5 Torr NH_3 pressure, but changes to 3.5 s^(−1) for 1 atm, values close (within 6%) to the ones on Fe(111). The experimental ratio between (211) and (111) rates at low (undisclosed) NH_3 pressure was reported to be 0.75. The excellent agreement with experiment on two very different surfaces and reaction mechanisms is a testament of the accuracy of QM modeling. In addition, our kinetic analysis indicates that Fe(211)R is more active than Fe(111) at high pressure, close to HB industrial conditions, and that (211)R is more abundant than (111) via a steady-state Wulff construction under HB conditions. Thus, at variance with common thinking, we advocate the Fe(211)R surface as the catalytically active phase of pure iron ammonia synthesis catalyst under HB industrial conditions.


Item Type:Article
Related URLs:
URLURL TypeDescription
https://doi.org/10.1039/c9cp01611bDOIArticle
ORCID:
AuthorORCID
Fuller, Jon0000-0003-1233-7842
Fortunelli, Alessandro0000-0001-5337-4450
Goddard, William A., III0000-0003-0097-5716
An, Qi0000-0003-4838-6232
Additional Information:© 2019 the Owner Societies. Received 22nd March 2019, Accepted 14th May 2019, First published on 14th May 2019. This work was supported by the 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 (program manager Dickson Ozokwelu, in collaboration with Idaho National Laboratories, Rebecca Fushimi). A. F. gratefully acknowledges financial support from a Short-Term Mission (STM) funded by Italian Consiglio Nazionale delle Ricerche (CNR). We would like to thank the Information Technology department at the University of Nevada, Reno for computing time on the High Performance Computing Cluster (Pronghorn). Some calculations were also carried out on a GPU-cluster provided by DURIP (Cliff Bedford, program manager). Authors contributions: AF, WAG and QA designed the strategy of this work. JF and QA performed QM calculations. AF performed kMC simulations. All authors wrote the paper. The authors declare no competing financial interest.
Group:Astronomy Department
Funders:
Funding AgencyGrant Number
Department of Energy (DOE)DE-AC07-05ID14517
Consiglio Nazionale delle Ricerche (CNR)UNSPECIFIED
Other Numbering System:
Other Numbering System NameOther Numbering System ID
WAG1336
Issue or Number:21
Record Number:CaltechAUTHORS:20190521-110908971
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20190521-110908971
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:95642
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:21 May 2019 18:20
Last Modified:03 Oct 2019 21:15

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