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Title: Proton Management as a Design Principle for Hydrogenase-inspired Catalysts

Abstract

The properties of the hydrogenase-inspired [Ni(PNP){sub 2}]{sup 2+} (PNP = Et{sub 2}PCH{sub 2}NMeCH{sub 2}PEt{sub 2}) catalyst for homogeneous hydrogen oxidation in acetonitrile solution are explored from a theoretical perspective for hydrogen production. The defining characteristic of this catalyst is the presence of pendent bases in the second coordination sphere that function as proton relays between the solution and the metal center. DFT calculations of the possible intermediates along proposed catalytic pathways are carried out and used to construct coupled Pourbaix diagrams of the redox processes and free-energy profiles along the reaction pathways. Analysis of the coupled Pourbaix diagrams reveals insights into the intermediate species and the mechanisms favored at different pH values of the solution. Consideration of the acid-base behavior of the metal hydride and H{sub 2} adduct species imposes additional constraints on the reaction mechanism, which can involve intramolecular as well as intermolecular proton-coupled electron-transfer steps. The efficacy of the catalyst is shown to depend critically on the pK{sub a} values of these potential intermediates, as they control both the species in solution at a given pH and the free-energy profile of reaction pathways. Optimal relationships among these pK{sub a} values can be identified, and it is demonstrated thatmore » 'proton management', i.e., the manipulation of these pK{sub a} values (e.g., through choice of metal or substituents on ligands), can serve as a design principle for improved catalytic behavior.« less

Authors:
; ; ;
Publication Date:
Research Org.:
Brookhaven National Lab. (BNL), Upton, NY (United States)
Sponsoring Org.:
USDOE SC OFFICE OF SCIENCE (SC)
OSTI Identifier:
1040518
Report Number(s):
BNL-94758-2011-JA
Journal ID: ISSN 1754-5692; R&D Project: CO-004; CO-026; TRN: US201210%%694
DOE Contract Number:  
DE-AC02-98CH10886
Resource Type:
Journal Article
Journal Name:
Energy and Environmental Science
Additional Journal Information:
Journal Volume: 4; Journal Issue: 8; Journal ID: ISSN 1754-5692
Country of Publication:
United States
Language:
English
Subject:
08 HYDROGEN; 37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; ACETONITRILE; ADDUCTS; CATALYSTS; DESIGN; ELECTRON TRANSFER; FREE ENERGY; HYDRIDES; HYDROGEN; HYDROGEN PRODUCTION; MANAGEMENT; OXIDATION; PH VALUE; PROTONS; REACTION KINETICS

Citation Formats

Muckerman, J T, Small, Y A, DuBois, D L, and Fujita, E. Proton Management as a Design Principle for Hydrogenase-inspired Catalysts. United States: N. p., 2011. Web.
Muckerman, J T, Small, Y A, DuBois, D L, & Fujita, E. Proton Management as a Design Principle for Hydrogenase-inspired Catalysts. United States.
Muckerman, J T, Small, Y A, DuBois, D L, and Fujita, E. Mon . "Proton Management as a Design Principle for Hydrogenase-inspired Catalysts". United States.
@article{osti_1040518,
title = {Proton Management as a Design Principle for Hydrogenase-inspired Catalysts},
author = {Muckerman, J T and Small, Y A and DuBois, D L and Fujita, E},
abstractNote = {The properties of the hydrogenase-inspired [Ni(PNP){sub 2}]{sup 2+} (PNP = Et{sub 2}PCH{sub 2}NMeCH{sub 2}PEt{sub 2}) catalyst for homogeneous hydrogen oxidation in acetonitrile solution are explored from a theoretical perspective for hydrogen production. The defining characteristic of this catalyst is the presence of pendent bases in the second coordination sphere that function as proton relays between the solution and the metal center. DFT calculations of the possible intermediates along proposed catalytic pathways are carried out and used to construct coupled Pourbaix diagrams of the redox processes and free-energy profiles along the reaction pathways. Analysis of the coupled Pourbaix diagrams reveals insights into the intermediate species and the mechanisms favored at different pH values of the solution. Consideration of the acid-base behavior of the metal hydride and H{sub 2} adduct species imposes additional constraints on the reaction mechanism, which can involve intramolecular as well as intermolecular proton-coupled electron-transfer steps. The efficacy of the catalyst is shown to depend critically on the pK{sub a} values of these potential intermediates, as they control both the species in solution at a given pH and the free-energy profile of reaction pathways. Optimal relationships among these pK{sub a} values can be identified, and it is demonstrated that 'proton management', i.e., the manipulation of these pK{sub a} values (e.g., through choice of metal or substituents on ligands), can serve as a design principle for improved catalytic behavior.},
doi = {},
journal = {Energy and Environmental Science},
issn = {1754-5692},
number = 8,
volume = 4,
place = {United States},
year = {2011},
month = {8}
}