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Computational Investigation of Small Molecule Catalysis by Cobalt, Rhodium, and Iridium Molecular Catalysts

Citation

Johnson, Samantha Jo Iva (2017) Computational Investigation of Small Molecule Catalysis by Cobalt, Rhodium, and Iridium Molecular Catalysts. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/Z9TD9V9K. http://resolver.caltech.edu/CaltechTHESIS:12082016-154933538

Abstract

Global energy demands are predicted to increase through 2040. In the spirit of meeting these demands, work focusing on increasing the efficiency of existing energy technologies, as well as improving energy storage is necessary. This work takes a catalytic approach to these challenges, focusing on Co, Rh, and Ir catalysts with pincer and bipyridine ligands. Density functional theory (DFT) can be used in order to gain a deeper understanding of how these catalysts behave. In the realm of improving existing technologies, the mechanism for oxidation of methane to methanol by Phebox Ir (Phebox = bis(oxazolinyl)phenyl) is investigated with a focus on understanding how subtle substitutions to the ligand can help or hinder this reaction. It is shown that in this catalyst, two unwanted intermediates on the potential energy surface (an IrIV state leading to catalyst deactivation and an IrV state leading to over-oxidation) can potentially be avoided by adding trifluoromethyl groups to the ligand. For production of fuels from solar energy, two reactions are studied. Experimentally, CO2 reduction to formate by (POCOP)Ir (POCOP = C6H3-2,6-[OP(tBu)2]2) has been shown to selectively occur at moderate potentials. The mechanism by which this catalyst reduces CO2 is elucidated. In particular, the impressive product selectivity afforded this catalyst for formate over hydrogen production is rooted in kinetics: high barriers for protonation inhibit the creation of H2 adducts. In addition to this, substitutions to the ligand and metal center are investigated to further illuminate the relationship between kinetics and thermodynamics. Hydrogen evolution in Cp*Rh(bpy) (bpy = 2,2'-bipyridine, Cp* = pentamethylcyclopentadienyl) is investigated, centering on unexpected protonation at the Cp* ligand rather than the metal center. This state is on the path for hydrogen evolution in the case of using weak acids, but in the presence of strong acids, the path through the traditional hydride is most likely. Finally, the attachment of these catalysts to electrode surfaces is discussed with the aim of making molecular catalysts a more viable option in industry It is shown that chlorine present in the attachment process enables easy catalyst dissociation from the surface. Several non-halogen options are discussed as replacements. Throughout the thesis two themes emerge: the constant interaction between thermodynamics and kinetics to control mechanistic paths and products, and the ability of small modifications to have huge impacts on catalytic cycles.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:catalysis, density functional theory, surface attachment, CO2 reduction, hydrogen evolution, hydricities
Degree Grantor:California Institute of Technology
Division:Engineering and Applied Science
Major Option:Materials Science
Thesis Availability:Mixed availability, specified at file level
Research Advisor(s):
  • Goddard, William A., III
Group:Materials and Process Simulation Center
Thesis Committee:
  • Goddard, William A., III (chair)
  • Gray, Harry B.
  • Faber, Katherine T.
  • Greer, Julia R.
  • Persson, Petter
Defense Date:2 December 2016
Non-Caltech Author Email:samanthajo.johnson (AT) gmail.com
Funders:
Funding AgencyGrant Number
National Science Foundation Graduate Research FellowshipDGE-1144469
Resnick Sustainability Institute Graduate Research FellowshipUNSPECIFIED
Record Number:CaltechTHESIS:12082016-154933538
Persistent URL:http://resolver.caltech.edu/CaltechTHESIS:12082016-154933538
DOI:10.7907/Z9TD9V9K
Related URLs:
URLURL TypeDescription
http://dx.doi.org/10.1021/ic5021725DOIArticle adapted for ch. 4
http://dx.doi.org/10.1021/acs.organomet.5b00200DOIArticle adapted for ch. 1
http://dx.doi.org/10.1073/pnas.1606018113DOIArticle adapted for ch. 5
http://dx.doi.org/10.1021/acscatal.6b01755DOIArticle adapted for ch. 3
ORCID:
AuthorORCID
Johnson, Samantha Jo Iva0000-0001-6495-9892
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:9991
Collection:CaltechTHESIS
Deposited By: Samantha Jo Johnson
Deposited On:15 Dec 2016 23:48
Last Modified:25 Aug 2017 17:37

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