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Access Type
WSU Access
Date of Award
January 2022
Degree Type
Dissertation
Degree Name
Ph.D.
Department
Chemistry
First Advisor
Claudio Verani
Abstract
ABSTRACTINVESTIGATING BIMETALLIC CATALYSIS THROUGH WATER SPLITTING AND ALCOHOL OXIDATION by Fredricka F. Morgan September 2022 Advisor: Prof. Claudio N. Verani Major: Chemistry (Inorganic) Degree: Doctor of Philosophy The challenging nature of water splitting makes it necessary for metal catalysts to be developed to lower the activation energy for these reactions to take place. In recent years, the study of earth abundant catalysts towards water splitting has gained a lot of attention by researchers. We have used homobimetallic cobalt, nickel, and zinc complexes designed with a pending arm bicompartmental ligand to experimentally and theoretically study cooperativity amongst earth abundant bimetallic catalysts towards water reduction. The zinc complex acts as a control to enable us to determine whether catalysis seen in cobalt and nickel are metal based. The redox-inactive 3d10 ZnII ion was not active and allowed us to rule out ligand-based catalysis. The cobalt and the nickel compounds are catalytic towards water reduction, although they rely on distinct pathways to produce H2. The metal-based oxidation processes seen in the cyclic voltammogram for the homobimetallic cobalt complex gave an indication that there is a possibility of oxidizing CoIII to higher oxidation states. This led to the experimental and theoretical evaluation of the catalytic nature of the homobimetallic cobalt complex towards electrocatalytic and chemical water oxidation. The cobalt complex is electro- and chemically catalytic with a TON of <5. Post catalytic analyses show that the catalysis is molecular. Isotopic labeling studies using H218O and KHS16O5 reveals that stoichiometrically labelled oxygen (18O2) is initially formed. This is indicative of the fact that both oxygen atoms in O2 formed during oxygen evolution originates from the water, confirming molecularity of the catalyst. The decrease of 18O2 while 18/16O increases with time shows the deviation from molecularity which is confirmed by DLS, SEM/EDS and XPS. DFT calculations reveal several PCET pathways leading to the evolution of oxygen. It also exhibits the uninvolvement of metal and the involvement of ligand in the mechanism of water oxidation. This is confirmed by XPS results which shows that there is no change in the oxidation state of cobalt after 60 minutes of catalysis. The oxidation of alcohols into its carbonylic products (aldehydes and ketones) is a very essential organic transformation since these products are useful in several chemical and pharmaceutical industries. Inspired by copper-containing enzymes such as galactose oxidase and catechol oxidase, in which distinct coordination environments and nuclearities lead to specific catalytic activities, the catalytic properties of a dinuclear and a mononuclear copper species towards benzyl alcohol oxidation using a multivariate statistical approach is investigated. The new dinuclear L1CuII2(-Pz)2](ClO4)3 is compared against the mononuclear L2CuII, where (L1)- and (L2)- are the respective deprotonated forms of 2,6-bis((bis(pyridin-2-ylmethyl)amino)methyl)-4-methylphenol, and 3-((bis(pyridin-2-ylmethyl)amino)methyl)-2-hydroxy-5-methylbenzaldehyde and (pz)- is a pyrazolato bridge. Copper (II) perchlorate (CP) is used as control. The catalytic oxidation of benzyl alcohol is pursued, aiming to assess the role of ligand environment and nuclearity. The multivariate statistical approach was selected to allow for the optimal conditions, considering variables such as catalyst load, hydrogen peroxide load, and time. L1CuII2(-Pz)2](ClO4)3 , L2CuII , and CP promoted selective production of benzaldehyde at different yields, with only negligible amounts of benzoic acid. Under normalized conditions, L2CuII showed superior catalytic activity. This species is 3.5-fold more active than the equally monometallic aqueous Cu (II) ion in CP and points out to the efficiency of the ligand framework. It is nearly 6-fold more active than the dinuclear L1CuII2(-Pz)2](ClO4)3, and indicates the favored nuclearity for the conversion of alcohols into aldehydes.
Recommended Citation
Morgan, Fredricka F., "Investigating Bimetallic Catalysis Through Water Splitting And Alcohol Oxidation" (2022). Wayne State University Dissertations. 3763.
https://digitalcommons.wayne.edu/oa_dissertations/3763