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Title: Reaction Mechanism and Kinetics for Ammonia Synthesis on the Fe(111) Surface

Here, the Haber-Bosch industrial process for synthesis of ammonia (NH 3) from hydrogen and nitrogen produces the millions of tons of ammonia gas annually needed to produce nitrates for fertilizers required to feed the earth’s growing populations. This process has been optimized extensively, but it still uses enormous amounts of energy (2% of the world’s supply), making it essential to dramatically improve its efficiency. To provide guidelines to accelerate this improvement, we used quantum mechanics to predict reaction mechanisms and kinetics for NH 3 synthesis on Fe(111)—the best Fe single crystal surface for NH 3 synthesis. We predicted the free energies of all reaction barriers for all steps in the mechanism and built these results into a kinetic Monte Carlo model for predicting steady state catalytic rates to compare with single-crystal experiments at 673 K and 20 atm. We find excellent agreement with a predicted turnover frequency (TOF) of 17.7 s –1 per 2 × 2 site (5.3 × 10 –9 mol/cm2/sec) compared to TOF = 10 s –1 per site from experiment.
Authors:
 [1] ; ORCiD logo [2] ; ORCiD logo [3] ;  [1] ; ORCiD logo [1]
  1. California Inst. of Technology (CalTech), Pasadena, CA (United States)
  2. California Inst. of Technology (CalTech), Pasadena, CA (United States); Univ. of Nevada - Reno, Reno, NV (United States)
  3. California Inst. of Technology (CalTech), Pasadena, CA (United States); CNR-ICCOM, Pisa (Italy)
Publication Date:
Report Number(s):
DOE-CALTECH-0000552
Journal ID: ISSN 0002-7863
Grant/Contract Number:
AR0000552
Type:
Accepted Manuscript
Journal Name:
Journal of the American Chemical Society
Additional Journal Information:
Journal Volume: 140; Journal Issue: 20; Journal ID: ISSN 0002-7863
Publisher:
American Chemical Society (ACS)
Research Org:
California Inst. of Technology (CalTech), Pasadena, CA (United States)
Sponsoring Org:
USDOE Office of Energy Efficiency and Renewable Energy (EERE)
Contributing Orgs:
Caltech
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; catalysis mechanism
OSTI Identifier:
1490875

Qian, Jin, An, Qi, Fortunelli, Alessandro, Nielsen, Robert J., and Goddard, III, William A.. Reaction Mechanism and Kinetics for Ammonia Synthesis on the Fe(111) Surface. United States: N. p., Web. doi:10.1021/jacs.7b13409.
Qian, Jin, An, Qi, Fortunelli, Alessandro, Nielsen, Robert J., & Goddard, III, William A.. Reaction Mechanism and Kinetics for Ammonia Synthesis on the Fe(111) Surface. United States. doi:10.1021/jacs.7b13409.
Qian, Jin, An, Qi, Fortunelli, Alessandro, Nielsen, Robert J., and Goddard, III, William A.. 2018. "Reaction Mechanism and Kinetics for Ammonia Synthesis on the Fe(111) Surface". United States. doi:10.1021/jacs.7b13409.
@article{osti_1490875,
title = {Reaction Mechanism and Kinetics for Ammonia Synthesis on the Fe(111) Surface},
author = {Qian, Jin and An, Qi and Fortunelli, Alessandro and Nielsen, Robert J. and Goddard, III, William A.},
abstractNote = {Here, the Haber-Bosch industrial process for synthesis of ammonia (NH3) from hydrogen and nitrogen produces the millions of tons of ammonia gas annually needed to produce nitrates for fertilizers required to feed the earth’s growing populations. This process has been optimized extensively, but it still uses enormous amounts of energy (2% of the world’s supply), making it essential to dramatically improve its efficiency. To provide guidelines to accelerate this improvement, we used quantum mechanics to predict reaction mechanisms and kinetics for NH3 synthesis on Fe(111)—the best Fe single crystal surface for NH3 synthesis. We predicted the free energies of all reaction barriers for all steps in the mechanism and built these results into a kinetic Monte Carlo model for predicting steady state catalytic rates to compare with single-crystal experiments at 673 K and 20 atm. We find excellent agreement with a predicted turnover frequency (TOF) of 17.7 s–1 per 2 × 2 site (5.3 × 10–9 mol/cm2/sec) compared to TOF = 10 s–1 per site from experiment.},
doi = {10.1021/jacs.7b13409},
journal = {Journal of the American Chemical Society},
number = 20,
volume = 140,
place = {United States},
year = {2018},
month = {4}
}