| Summary: | Atmospheric carbon dioxide (CO₂) concentrations have increased rapidly in recent decades due to the burning of fossil fuels, deforestation, and other industrial practices. The excessive accumulation of CO₂ in the atmosphere leads to global warming, ocean acidification, and other environmental imbalances, which may ultimately have wider societal implications. One potential solution to closing the carbon cycle is utilizing CO₂, rather than fossil fuels, as the carbon source for fuels and chemicals production. This lowers atmospheric CO₂ levels while simultaneously providing an economic incentive for capturing and converting CO₂ into more valuable products. This dissertation includes studies on three hybrid catalytic reactor systems coupling electrochemistry, thermochemistry, and plasma chemistry for the conversion of CO₂ into value-added oxygenates, such as methanol and C3 oxygenates (propanal and 1-propanol). First, a tandem two-stage system is described where CO₂ is electrochemically reduced into syngas followed by the thermochemical methanol synthesis reaction. The work here specifically focuses on the electrochemical CO₂ reduction reaction to produce syngas with tunable H₂/CO ratios. Using a combination of electrochemical experiments, in-situ characterization, and density functional theory calculations, palladium-, gold-, and silver-modified transition metal carbides and nitrides were found to be promising catalysts for enhancing electrochemical activity while reducing the overall precious metal loading. Second, another tandem two-stage system is demonstrated where CO₂ is electrochemically reduced into ethylene and syngas followed by the thermochemical hydroformylation reaction to produce propanal and 1-propanol. The CO₂ electrolyzer was evaluated with Cu catalysts containing different oxidation states and with modifications to the gas diffusion layer hydrophobicity, while the hydroformylation reactor was tested over a Rh₁Co₃/MCM-41 catalyst. The tandem configuration achieved a C₃ oxygenate selectivity of ...
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