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Thesis advisor: Udayan Mohanty / Metal-oxygen batteries recently emerge as one of the most promising post-Li-ion energy storage technologies. The key feature of this technology lies in the conversion reactions of O2 at the cathode. Such a chemistry promises the highest theoretical energy densities due to the contribution from the cathode reactions. However, the conversion between various oxygen-based species suffer severe kinetic penalties, resulting in poor energy efficiencies and low rate capabilities. To promote these reactions, catalysts with desired functionality and stability are needed. On the other hand, the O2-based chemistry incurs severe parasitic chemical reactions against various cell components, including the anode, the cathode and the electrolyte. Consequently, the reported cyclabilities of metal-oxygen batteries remain much worse than required. While stable cathode and anode candidates have been developed, further advance of this technology still hinges on developing stable electrolyte and efficient catalyst to ensure prolonged and stable cell operations. In the first part of this thesis, two distinct strategies were exploited as proof-of-concept demonstrations on the catalyst design for metal-oxygen batteries. For one, using Li-O2 batteries as a study platform, we show that the stability of catalyst can be heavily dependent on the synthesis history. A novel approach, namely carbothermal shock method, was found to enable superior chemical and structural stability of the catalyst compared to those of the catalyst prepared by conventional methods. For another, using Mg-O2 batteries as prototypical system, we demonstrate a strategy using two redox mediators that concertedly operate for discharge and recharge. As a result, a total overpotential reduction by ca. 600 mV can be achieved through manipulating the charge transfer mechanism. To meet the need of a stable electrolyte for metal-oxygen batteries, in the second part of this thesis, we analyzed the decomposition pathways of the electrolyte in the presence of reactive oxygen species. Using Li-O2 battery as a model system, we address this issue by employing a water-in-salt (WiS) electrolyte that eliminates organic solvents all together. WiS was found stable under Li-O2 battery operation conditions. When carbon was used as a cathode, much longer cycling numbers (>70) can be achieved in WiS than in organic ones. When carbon was replaced with a carbon-free cathode (TiSi2 nanonets decorated with Ru catalyst), over 300 reversible cycles was measured. The unique feature of WiS also enables other opportunities beyond O2 chemistry in metal-oxygen batteries. Toward the end of this thesis, we employ WiS for electrochemical CO2 reduction reactions. By controlling the concentration of H2O in WiS, the rate determining step on Au catalyst was found to be the first electron transfer from the electrode to CO2. Moreover, the reduced H2O activity by WiS significantly suppressed hydrogen evolution reactions, through which high selectivity toward CO can be measured. Our study provides important knowledge base on the design of electrolyte for future optimizations. / Thesis (PhD) — Boston College, 2019. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Chemistry.

Doctor of Science in Engineering - Engineering / Transalkylation, a process of transfer of alkyl groups from one aromatic compound to another is carried out on acidic catalysts such as zeolites. The porous nature of zeolites is a prohibiting factor for transalkylation involving highly conjugated aromatic compounds. The study looks at the production of humic acids as well as their evaluation as potential acid catalysts for transalkylation. Optimisation of the production of humic acids was carried out through determination of a suitable coal type using air oxidation. Slurry phase oxidation was used to enhance and optimise coal oxidation and the production of humic acids. From the characterisations and test reactions carried out, humic acids do show some catalytic properties; however the study also showed that the strength of the acid sites is not strong enough to induce transalkylation reactions. Investigations of using humic acids as catalysts for other reactions such as oxidative dehydrogenation of ethylbenzene to form styrene, is recommended.

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My research is focused on two main objectives, the study of catalytic efficiency and mechanism of palladium nanoparticles stabilized by poly(vinylpyrrolidone) (PVP) for carbon-carbon coupling reactions, and to rationally synthesize metal nanoparticles stabilized by metal-carbon bonds and apply them to catalyze carbon-carbon coupling reactions.<p> In the first project, Pd nanoparticles stabilized by PVP were used to catalyze carbon-coupling reactions, specifically the Stille and Suzuki reactions. The mechanism of carbon-carbon coupling reactions was studied. The uncertainty of whether nanoparticles or Pd salts are the catalyst was also examined using the same experimental procedure with Pd salts to examine their catalytic activity in carbon-carbon coupling reactions. Results show that the presence of O2 is crucial to the Stille reaction with the Pd nanoparticles, which are nearly completely inert under N2, while the K2PdCl4 precursor is itself quite active for the Stille reaction. However, the Pd nanoparticles were found to be active for the Suzuki reaction with high yields in the absence of O2. The yields for 4-chlorobenzoic acid are higher than 4-bromobenzoic acid and occur for un-catalyzed reactions, for reasons that are still unknown. Finally Au nanoparticles have been tested by the same experimental procedure and have no catalytic activity for these two reactions.<p> In the second project, the synthesis of Au and Pd monolayer protected clusters (MPCs) with metal carbon covalent linkages was examined, and the stability of the resulting MPCs was tested. UV-Vis spectra and TEM images show the formation of Au and Pd nanoparticles and 1H NMR was used to characterize the ligands attached to the surface of the nanoparticles. The decylphenyl-stabilized Pd MPCs were synthesized successfully and quite stable in air, while decylphenyl-stabilized Au MPCs prepared with the same protocol have less stability and are easily decomposed. XPS spectra indicate the composition of decylphenyl-stabilized Pd MPCs is a combination of Pd0 and Pd2+ species with the Pd2+ species in excess. In addition, alkylphenyl-stabilized Pd nanoparticles were shown to be effective catalysts for carbon-carbon coupling reactions such as Suzuki and Stille reactions as well as hydrogenation reactions. Finally, it was noted that Pd-C bonds could be easily reduced by H2 when performing hydrogenation reactions resulting in nanoparticle aggregation and precipitation under hydrogenation conditions.

My research is focused on two main objectives, the study of catalytic efficiency and mechanism of palladium nanoparticles stabilized by poly(vinylpyrrolidone) (PVP) for carbon-carbon coupling reactions, and to rationally synthesize metal nanoparticles stabilized by metal-carbon bonds and apply them to catalyze carbon-carbon coupling reactions.<p> In the first project, Pd nanoparticles stabilized by PVP were used to catalyze carbon-coupling reactions, specifically the Stille and Suzuki reactions. The mechanism of carbon-carbon coupling reactions was studied. The uncertainty of whether nanoparticles or Pd salts are the catalyst was also examined using the same experimental procedure with Pd salts to examine their catalytic activity in carbon-carbon coupling reactions. Results show that the presence of O2 is crucial to the Stille reaction with the Pd nanoparticles, which are nearly completely inert under N2, while the K2PdCl4 precursor is itself quite active for the Stille reaction. However, the Pd nanoparticles were found to be active for the Suzuki reaction with high yields in the absence of O2. The yields for 4-chlorobenzoic acid are higher than 4-bromobenzoic acid and occur for un-catalyzed reactions, for reasons that are still unknown. Finally Au nanoparticles have been tested by the same experimental procedure and have no catalytic activity for these two reactions.<p> In the second project, the synthesis of Au and Pd monolayer protected clusters (MPCs) with metal carbon covalent linkages was examined, and the stability of the resulting MPCs was tested. UV-Vis spectra and TEM images show the formation of Au and Pd nanoparticles and 1H NMR was used to characterize the ligands attached to the surface of the nanoparticles. The decylphenyl-stabilized Pd MPCs were synthesized successfully and quite stable in air, while decylphenyl-stabilized Au MPCs prepared with the same protocol have less stability and are easily decomposed. XPS spectra indicate the composition of decylphenyl-stabilized Pd MPCs is a combination of Pd0 and Pd2+ species with the Pd2+ species in excess. In addition, alkylphenyl-stabilized Pd nanoparticles were shown to be effective catalysts for carbon-carbon coupling reactions such as Suzuki and Stille reactions as well as hydrogenation reactions. Finally, it was noted that Pd-C bonds could be easily reduced by H2 when performing hydrogenation reactions resulting in nanoparticle aggregation and precipitation under hydrogenation conditions.