Partial Oxidation of Hydrocarbons Over Ceria Zirconia Catalysts
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This thesis describes research along several avenues pertaining to oxidation reactions. First, the major conclusions are summarized from a perspective describing active oxygen species on catalyst surfaces. Some oxygen species are more selective than others and if these species were better understood, a catalyst surface could be tuned to produce those selective species instead of unselective ones. However, these species readily interconvert and there does not exist a single analytical method which can characterize—and differentiate—between all of the possible species. Due to this situation, analytical techniques are focused upon in that paper. The most promising analytical technique is isotope exchange coupled with infrared spectroscopy and an inline mass spectrometer. Next, methane partial oxidation over ceria zirconia catalysts is studied with infrared spectroscopy. Methane and oxygen concentrations are modulated to differentiate active and spectator species via modulation excitation spectroscopy. Aromatic and alkoxy surface species modulate in sync with each other, supporting the hypothesis that these species compete with each other in the partial oxidation of methane to methanol; formates are formed in all cases, and these species are associated with the complete combustion of methane to carbon dioxide and water. Chemical looping may be an appropriate reaction engineering method to increase the yield of selective oxidation products since the formate and alkoxy species were separated during the oxygen modulation experiment over nickel-copper on ceria zirconia. Finally, two reactions (water splitting and heptane partial oxidation) catalyzed under mechanical forces are explored. It was hypothesized that oxygen could be mechanically driven from the ceria lattice. Oxygen from water would then replenish the lattice, releasing hydrogen. Due to iron contamination from the steel vessel, this hypothesis cannot be confirmed. Ceria zirconia, when milled in the presence of heptane, exhibits infrared bands in the C-O stretching region, leading to the conclusion that some sort of oxidative reaction occurs during milling. Additional study needs be performed to describe this system fully.