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Type of Document Dissertation Author Schuyten, Stephen J URN etd-02182008-155212 Title ACTIVITY AND IN-SITU XAS STUDIES OF PROMOTED COPPER AND ZINC OXIDE CATALYSTS FOR HYDROGEN PRODUCTION BY METHANOL PARTIAL OXIDATION Degree Doctor of Philosophy Department Chemical Engineering Advisory Committee
Advisor Name Title Alexander Mukasyan Committee Member Eduardo. E. Wolf Committee Member Jeffrey T. Miller Committee Member Paul McGinn Committee Member William F. Schneider Committee Member Keywords
- palladium
- copper
- partial oxidation
- methanol reforming
Date of Defense 2008-02-13 Availability unrestricted Abstract A three step high throughput catalytic screening process was used to evaluate the activity and selectivity of copper and zinc based methanol partial oxidation catalysts. The most active catalyst preparations contained both palladium and zirconium promoters. The high activity and selectivity obtained from the doubly promoted 7Cu/3Zn/1Zr-1Pd composition suggested a synergy between palladium and zirconium promoters.
Characterization studies showed that the zirconia promoter significantly enhanced characteristics such as surface area, dispersion, crystallite size, and deactivation resistance, leading to lowered reduction temperature. However the zirconia promoter alone only slightly lowered the reaction light off temperature. Unlike zirconia, the palladium promoter did not significantly alter microstructural characteristics of the catalyst. Palladium was shown to significantly lower the reduction temperature regardless of initial CuO crystallite size, which suggests that palladium enhances the catalytic activity by increasing copper reducibility. Copper K edge x-ray absorption spectroscopy confirmed palladium promoted catalysts are more easily reduced to Cu0 under reaction conditions. Palladium x-ray absorption spectroscopy was used to determine that formation of Pd-Cu alloys is preferred over Pd-Zn alloys.
Using a four step model reaction pathway it was found that the combination of palladium and zirconia promoters significantly lowers the activation energy of the methanol combustion and steam reforming reactions. However, promoter materials do not influence the methanol decomposition and water gas shift activation energies because of the similarity of catalyst state at high reaction temperatures regardless of promoter materials. In reformer simulations it was found that approximately 5 grams of catalyst is needed to power a notebook computer.
Combustion synthesized catalysts were shown to have activity similar to bulk prepared catalysts, despite lower copper area, suggesting higher turn over rate. It was found that changing the palladium loading to the surface from the bulk did not significantly affect catalytic activity, most likely due to encapsulation of Pd by alloying with copper. An exploration of preparing structured catalysts by hydrothermal synthesis methods showed that intimate contact of copper with certain oxide phases is required for high activity.
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