Characterization of copper/zinc-oxide catalysts for methanol reformation.
AuthorGoodby, Brian Edward.
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PublisherThe University of Arizona.
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AbstractThe research presented in this dissertation involved characterization of the Cu/ZnO solid catalyst system as applied to methanol/steam reformation. Thermogravimetry was used to investigate in-lab synthesized samples and a commercial product G66B (Cu/ZnO 33/67 wt. %). The 33% Cu sample contained Cu ions in the ZnO matrix. This phase required the highest temperatures (400°C) for H₂ reduction. The 50% Cu sample reduced at a lower temperature (220°C) but its complete reduction required the same maximum temperature. The higher temperature process was similar to the 33% case, while the lower one was due to the reduction of a amorphous CuO phase. The 66% Cu sample reduced in a fairly narrow low temperature (270°C) range. Therefore, its CuO phase has a amorphous structure. G55B reduced at lower temperatures than the in-lab samples. This difference is possibly due to different synthetic procedures used in the production of G66B and the in-lab samples. The CuO phase of G66B appears to be amorphous and well dispersed. Raman spectroscopy was used to identify the crystal phases of these solids. The complexity of the initial precipitate was monitored versus the Cu/Zn ratio of the system. The nature of the phases present under reduction conditions was determined. This information has provided insight into the active phases involved in methanol reformation. The role of the solids lattice oxygen was determined. The reaction was carried out on labelled ¹⁸O-containing Cu/ZnO. Incorporation of ¹⁸O into both CO₂ and H₂O clearly indicates the involvement of these oxygens in the reaction. Observation of C¹⁸O¹⁸O indicates that the C-O bond in methanol does not remain intact. XPS was used to determine the effects of oxidation, reduction, and reaction on the Cu component of G66B. Upon oxidation all Cu exists as Cu⁺². The catalyst always contains Cu⁺¹ and Cuᵒ after H₂ reduction. After methanol/steam reformation with a 50/50 vol% mxiture, all Cu is reduced to Cuᵒ. Changes in the Cu/Zn ratio of the surface are interpreted in terms of changes in surface morphology.