Abstract
Using density functional theory (DFT), we studied the catalytic activity of iron oxide nanoclusters that mimic the structure of the active site in the soluble form of methane monooxygenase (sMMO) for the partial oxidation of methane to methanol. Using N2O as the oxidant, we consider a radical-rebound mechanism and a concerted mechanism for the oxidation of methane on either a bridging oxygen (Ob) or a terminal oxygen (Ot) active site. We find that the radical-rebound pathway is preferred over the concerted pathway by 40-50 kJ/mol, but the desorption of methanol and the regeneration of the oxygen site are found to be the highest barriers for the direct conversion of methane to methanol with these catalysts. As demonstrated by a population analysis, the Ox (x = b or t) site behaves as an oxygen radical during the H abstraction, and the [Fe+-Ox -] site behaves as a Lewis acid-base pair during the concerted C-H cleavage. Molecular orbital decomposition analysis further demonstrates electron transfer during the oxidation and reduction steps of the reaction. High-level multireference calculations were also carried out to further assess the DFT results. Understanding how these systems behave during the proposed reaction pathways provides new insights into how they can be tuned for methane partial oxidation.
| Original language | English (US) |
|---|---|
| Pages (from-to) | 1580-1592 |
| Number of pages | 13 |
| Journal | Journal of Physical Chemistry A |
| Volume | 124 |
| Issue number | 8 |
| DOIs | |
| State | Published - Feb 27 2020 |
Bibliographical note
Funding Information:This work was supported as part of the Inorganometallic Catalyst Design Center, an Energy Frontier Research Center funded by the U.S. Department of Energy (DOE), Office of Science, Basic Energy Sciences (BES), under Award DE-SC0012702. M.B. would like to thank the Quest High Performance Computing Cluster, which is maintained by the Northwestern University Information Technology, and the National Energy Research Scientific Computing Center, a DOE Office of Science User Facility supported by the Office of Science of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231. The authors acknowledge the Minnesota Supercomputing Institute (MSI) at the University of Minnesota for providing additional computational resources. M.B. would like to additionally thank the National Science Foundation for a Graduate Research Fellowship.
Funding Information:
This work was supported as part of the Inorganometallic Catalyst Design Center, an Energy Frontier Research Center funded by the U.S. Department of Energy (DOE), Office of Science, Basic Energy Sciences (BES), under Award DE-SC0012702. M.B. would like to thank the Quest High Performance Computing Cluster, which is maintained by the Northwestern University Information Technology, and the National Energy Research Scientific Computing Center, a DOE Office of Science User Facility supported by the Office of Science of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231. The authors acknowledge the Minnesota Supercomputing Institute (MSI) at the University of Minnesota for providing additional computational resources. M.B. would like to additionally thank the National Science Foundation for a Graduate Research Fellowship.
Publisher Copyright:
Copyright © 2020 American Chemical Society.