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Title: Optimizing Open Iron Sites in Metal–Organic Frameworks for Ethane Oxidation: A First-Principles Study

Abstract

Activation of the C-H bonds in ethane to form ethanol is a highly desirable, yet challenging, reaction. Metal- organic frameworks (MOFs) with open Fe sites are promising candidates for catalyzing this reaction. One advantage of MOFs is their modular construction from inorganic nodes and organic linkers, allowing for flexible design and detailed control of properties. In this work, we studied a series of single-metal atom Fe model systems with ligands that are commonly used as MOF linkers and tried to understand how one can design an optimal Fe catalyst. We found linear relationships between the binding enthalpy of oxygen to the Fe sites and common descriptors for catalytic reactions, such as the Fe 3d energy levels in different reaction intermediates. We further analyzed the three highest-barrier steps in the ethane oxidation cycle (including desorption of the product) with the Fe 3d energy levels. Volcano relationships are revealed with peaks toward higher Fe 3d energy and stronger electron-donating group functionalization of linkers. Furthermore, we found that the Fe 3d energy levels positively correlate with the electron-donating strength of functional groups on the linkers. Finally, we validated our hypotheses on larger models of MOF-74 iron sites. Compared with MOF-74, functionalizing the MOF-74more » linkers with NH 2 groups lowers the enthalpic barrier for the most endothermic step in the reaction cycle. Our findings provide insight for catalyst optimization and point out directions for future experimental efforts.« less

Authors:
 [1];  [2]; ORCiD logo [3]
+ Show Author Affiliations
  1. Northwestern Univ., Evanston, IL (United States); Purdue Univ., West Lafayette, IN (United States)
  2. Clemson Univ., SC (United States)
  3. Northwestern Univ., Evanston, IL (United States)
Publication Date:
Research Org.:
Northwestern Univ., Evanston, IL (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
OSTI Identifier:
1371789
Alternate Identifier(s):
OSTI ID: 1507736
Grant/Contract Number:  
SC0012702; AC02-05CH11231
Resource Type:
Published Article
Journal Name:
ACS Applied Materials and Interfaces
Additional Journal Information:
Journal Volume: 9; Journal Issue: 39; Journal ID: ISSN 1944-8244
Publisher:
American Chemical Society (ACS)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; 36 MATERIALS SCIENCE; catalyst screening; DFT; ethane; ethanol; metal−organic frameworks; nitrous oxide

Citation Formats

Liao, Peilin, Getman, Rachel B., and Snurr, Randall Q. Optimizing Open Iron Sites in Metal–Organic Frameworks for Ethane Oxidation: A First-Principles Study. United States: N. p., 2017. Web. doi:10.1021/acsami.7b02195.
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Liao, Peilin, Getman, Rachel B., & Snurr, Randall Q. Optimizing Open Iron Sites in Metal–Organic Frameworks for Ethane Oxidation: A First-Principles Study. United States. doi:10.1021/acsami.7b02195.
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Liao, Peilin, Getman, Rachel B., and Snurr, Randall Q. Mon . "Optimizing Open Iron Sites in Metal–Organic Frameworks for Ethane Oxidation: A First-Principles Study". United States. doi:10.1021/acsami.7b02195.
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@article{osti_1371789,
title = {Optimizing Open Iron Sites in Metal–Organic Frameworks for Ethane Oxidation: A First-Principles Study},
author = {Liao, Peilin and Getman, Rachel B. and Snurr, Randall Q.},
abstractNote = {Activation of the C-H bonds in ethane to form ethanol is a highly desirable, yet challenging, reaction. Metal- organic frameworks (MOFs) with open Fe sites are promising candidates for catalyzing this reaction. One advantage of MOFs is their modular construction from inorganic nodes and organic linkers, allowing for flexible design and detailed control of properties. In this work, we studied a series of single-metal atom Fe model systems with ligands that are commonly used as MOF linkers and tried to understand how one can design an optimal Fe catalyst. We found linear relationships between the binding enthalpy of oxygen to the Fe sites and common descriptors for catalytic reactions, such as the Fe 3d energy levels in different reaction intermediates. We further analyzed the three highest-barrier steps in the ethane oxidation cycle (including desorption of the product) with the Fe 3d energy levels. Volcano relationships are revealed with peaks toward higher Fe 3d energy and stronger electron-donating group functionalization of linkers. Furthermore, we found that the Fe 3d energy levels positively correlate with the electron-donating strength of functional groups on the linkers. Finally, we validated our hypotheses on larger models of MOF-74 iron sites. Compared with MOF-74, functionalizing the MOF-74 linkers with NH2 groups lowers the enthalpic barrier for the most endothermic step in the reaction cycle. Our findings provide insight for catalyst optimization and point out directions for future experimental efforts.},
doi = {10.1021/acsami.7b02195},
journal = {ACS Applied Materials and Interfaces},
number = 39,
volume = 9,
place = {United States},
year = {2017},
month = {4}
}
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Journal Article:
Free Publicly Available Full Text
Publisher's Version of Record
DOI: 10.1021/acsami.7b02195
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Cited by: 4 works
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Figures / Tables:

Figure 1. Figure 1.: Figure 1. (a) Ligand structures with complete and abbreviated names. Dashed lines in structures mark where atoms coordinate to Fe. Functional groups are indexed by numbers, where no prime symbol, a subsequent prime symbol, and a subsequent double prime symbol indicate para, meta, and ortho substitutions, respectively. Onlymore » single substitution on the linker is tested; therefore, when no ligand is specified for Rn (n = 1, 2, 3), Rn is the H atom. (b) Top view (looking from the missing ligand position toward the Fe site) for sample five-coordinated pyramidal A structures (see Figure 3) with labels underneath. Without and with a prime symbol after the ligand names correspond to anion ligands opposite to each other within the pyramidal plane (“PP” arrangement) and one of the anion ligands located at the pyramidal top (“PT” arrangement), respectively. Gray dashed circles indicate functional group substitutions. Color scheme: H, white; C, gray; N, blue; O, red; and Fe, purple. Figure S3 shows additional sample structures.« less
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