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Fe-mediated HER vs N_2RR: Exploring Factors that Contribute to Selectivity in P_3^EFe(N_2) (E = B, Si, C) Catalyst Model Systems

Matson, Benjamin D. and Peters, Jonas C. (2018) Fe-mediated HER vs N_2RR: Exploring Factors that Contribute to Selectivity in P_3^EFe(N_2) (E = B, Si, C) Catalyst Model Systems. ACS Catalysis, 8 (2). pp. 1448-1455. ISSN 2155-5435. https://resolver.caltech.edu/CaltechAUTHORS:20180104-140230786

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Abstract

Mitigation of the hydrogen evolution reaction (HER) is a key challenge in selective small molecule reduction catalysis. This is especially true of catalytic nitrogen (N_2) and carbon dioxide (CO_2) reduction reactions (N_2RR and CO_2RR, respectively) using H^+/e• currency. Here we explore, via DFT calculations, three iron model systems, P_3^EFe (E = B, Si, C), known to mediate both N_2RR and HER, but with different selectivity depending on the identity of the auxiliary ligand. It is suggested that the respective efficiencies of these systems for N_2RR trend with the predicted N–H bonds strengths of two putative hydrazido intermediates of the proposed catalytic cycle, P_3^EFe(NNH_2)^+ and P_3^EFe(NNH_2). Further, a mechanism is presented for undesired HER consistent with DFT studies, and previously reported experimental data, for these systems; bimolecular proton-coupled-electron-transfer (PCET) from intermediates with weak N–H bonds is posited as an important source of H_2, instead of more traditional scenarios that proceed via metal hydride intermediates and proton transfer/electron transfer (PT/ET) pathways. Wiberg bond indices provide additional insight into key factors related to the degree of stabilization of P_3^EFe(NNH_2) species, factors that trend with overall product selectivity.


Item Type:Article
Related URLs:
URLURL TypeDescription
https://dx.doi.org/10.1021/acscatal.7b03068DOIArticle
http://pubs.acs.org/doi/10.1021/acscatal.7b03068PublisherArticle
http://pubs.acs.org/doi/suppl/10.1021/acscatal.7b03068PublisherSupporting Information
ORCID:
AuthorORCID
Peters, Jonas C.0000-0002-6610-4414
Alternate Title:Fe-mediated HER vs N2RR: Exploring Factors that Contribute to Selectivity in P3EFe(N2) (E = B, Si, C) Catalyst Model Systems
Additional Information:© 2018 American Chemical Society. Received: September 7, 2017; Revised: January 3, 2018; Published: January 3, 2018. This work was supported by the NIH (GM 070757) and the Gordon and Betty Moore Foundation, and the Extreme Science and Engineering Discovery Environment (XSEDE), which is supported by National Science Foundation grant number ACI-1053575. B.D.M. acknowledges the support of the NSF for a Graduate Fellowship (GRFP). We thank Matthew Chalkley for insightful input. No competing financial interests have been declared.
Funders:
Funding AgencyGrant Number
NIHGM-070757
Gordon and Betty Moore FoundationUNSPECIFIED
NSFACI-1053575
NSF Graduate Research FellowshipUNSPECIFIED
Subject Keywords:nitrogen fixation, N_2RR, HER, hydrogen evolution, PCET, HAT, nitrogenase
Issue or Number:2
Record Number:CaltechAUTHORS:20180104-140230786
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20180104-140230786
Official Citation:Fe-Mediated HER vs N2RR: Exploring Factors That Contribute to Selectivity in P3EFe(N2) (E = B, Si, C) Catalyst Model Systems Benjamin D. Matson and Jonas C. Peters ACS Catalysis 2018 8 (2), 1448-1455 DOI: 10.1021/acscatal.7b03068
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:84084
Collection:CaltechAUTHORS
Deposited By: George Porter
Deposited On:04 Jan 2018 22:49
Last Modified:03 Oct 2019 19:14

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