Doctor of Philosophy (PhD)
The interest in converting synthesis gas to alcohols and oxygenated fuel additives via CO hydrogenation is growing rapidly due to the increasing rise in oil prices. Among the potential end products, ethanol is desirable since it serves as a clean alternative fuel, a gasoline blend, and a hydrogen carrier to supply fuel cells. The high cost and limited availability of the most active/selective Rh-based catalysts has led to the development of base metal catalysts such as modified Cu-based catalysts. Literature suggests that a combination of Co (or Mn) with Cu can facilitate higher alcohol formation by a non-dissociative adsorption of CO on the Cu sites, followed by insertion of CO into growing hydrocarbon chains formed from dissociated CO on the Co (or Mn) sites. The goal of this research work was to synthesize, characterize and test two types of copper-based catalysts – bimetallic nanoparticles and pyrochlores, for the hydrogenation of CO to higher alcohols, particularly ethanol. Copper-based bimetallic nanoparticles with core-shell morphologies synthesized using wet-chemical methods were the major focus of this dissertation. Uniformly dispersed and highly reproducible Cu core-Mn3O4 shell (Cu@Mn3O4) and Cu core-Co3O4 shell (Cu@Co3O4) nanoparticles were synthesized with a porous shell, thereby making the copper core accessible. DRIFTS (in-situ FTIR) showed that the Cu@Mn3O4 nanoparticles have a greater CO adsorption capacity and a lower CO dissociation activity, while the Cu@Co3O4 nanoparticles showed a higher selectivity towards alcohols and oxygenates, with the total alcohols/oxygenates being 48% of the total products. An ethanol selectivity of 15% (with a corresponding methane selectivity of 11%) was achieved at 10 bar, 270 °C and H2/CO=2. Another focus was on Cu-ZnO based catalysts supported on La2Zr2O7 pyrochlores which are believed to be promising candidates as supports for stable and active copper catalysts for CO hydrogenation. Mn or Co promoted Cu-ZnO-La2Zr2O7-Li2O catalysts were synthesized by coprecipitation. Addition of Mn or Co promoter increased the overall extent of reduction of the catalysts. DRIFTS studies showed increased CO chemisorption and negligible methanation on the Mn promoted catalyst under the conditions tested, while methane was the major product on the Co-promoted catalyst.
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Subramanian, Nachal Devi, "Catalytic Hydrogenation of CO to Higher Alcohols" (2011). LSU Doctoral Dissertations. 1914.
Spivey, James J.