Date of Award
Master of Science
In this work the performance of cerium-based oxygen carriers is investigated in a simulated chemical looping dry reforming system using methane and carbon dioxide as fuel and oxidizing gas respectively. The samples to be studied are pure cerium oxide and cerium oxide doped with zirconium, yttrium, samarium, and scandium more specifically: CeO2, Ce0.8Y0.2O1.9, Ce0.85Y0.05Zr0.1O1.975, Ce0.95Zr0.05O2, Ce0.9Sm0.05Zr0.05O1.975, and Ce0.9Sc0.05Zr0.05O1.975. Characteristics such as crystallography including lattice parameter and particle size of the samples are evaluated using X-ray diffraction (XRD) and particle size analysis. The oxygen transport capacity will also be measured using a thermogravimetric analyzer (TGA). This method of measurement also allowed for insight on oxygen release temperatures as well as recyclability of the samples. The particle size analysis showed that the synthesis method of precipitation-agglomeration resulted in samples with consistent particle size distribution indicating the method can be scaled up. The X-ray analysis of samples before and after the TGA tests show that all the materials tested had a cubic fluorite crystal structure which was maintained through the oxidation reduction cycles. The lattice parameter was found to increase slightly with a loss in oxygen content in the samples. The addition of trivalent dopants resulted in a decrease in the temperature of initiation of reduction in methane. While reduction of commercial ceria initiated near 800 oC. the addition of trivalent dopants resulted in a lowering of the initialization temperature between of 150 – 200oC. The activation energy of commercial ceria was 248.42 kJ/mol for reduction in methane, indicating that the rate controlling mechanism is chemical reaction rather than diffusion. The addition of trivalent dopants resulted in a significant lowering in the activation energy. The activation energies obtained in this study show that the addition of dopant increased the significance of diffusion through the solid and the controlling mechanisms were both diffusion and chemical reaction. Overall, the addition of trivalent dopants enhanced the extent of oxygen exchange in CLDR process.
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