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-74 linkers with NH2groups 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.
authors.affiliation: Department of Chemical & Biological Engineering, Northwestern University , Evanston, Illinois 60208, United States.|School of Materials Engineering, Purdue University , West Lafayette, Indiana 47907, United States.
authors.forename: Peilin
authors.initials: P
authors.lastname: Liao
authors.affiliation: Department of Chemical and Biomolecular Engineering, Clemson University , Clemson, South Carolina 29634, United States.
authors.forename: Rachel B
authors.initials: RB
authors.lastname: Getman
authors.affiliation: Department of Chemical & Biological Engineering, Northwestern University , Evanston, Illinois 60208, United States.
authors.forename: Randall Q
authors.identifier: http://orcid.org/0000-0003-2925-9246
authors.initials: RQ
authors.lastname: Snurr
keywords: DFT; catalyst screening; ethane; ethanol; metal−organic frameworks; nitrous oxide