Date of Award

2015

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Graduate Group

Chemical and Biomolecular Engineering

First Advisor

Raymond J. Gorte

Abstract

Interactions between metal catalysts and oxide supports have been known to be important in modifying the catalyst properties for many years, and catalysts with core-shell nanostructures are promising for optimizing these metal-oxide interactions. In this dissertation, core-shell nanoparticles that consist of a metal core and a metal-oxide shell were synthesized and deposited onto an alumina support. These core-shell catalysts exhibit unique catalytic and thermodynamic properties, and were investigated with different core-shell compositions as part of this thesis.

The first part of this dissertation focuses on a Pd@CeO2/Si-Al2O3 catalyst that has been developed and examined for methane-oxidation previously. To better understand this material, I investigated the catalytic, adsorption, and redox properties as they are related to the methane-steam-reforming. I also looked at the effect of calcination temperature on the catalytic properties since the catalysts were strongly influenced by the calcination temperatures, in a manner that is very different from that observed with conventional Pd/CeO2 catalysts. It was found that calcination to higher temperatures improved the performance of the Pd@CeO2 catalyst by modifying the redox properties of the ceria shell.

In the second part of this dissertation, the synthesis and investigation of core-shell catalysts was extended to other precious-metal cores and metal-oxide shells. To determine the effect of shell material, a Pd@ZrO2/Si-Al2O3 catalyst was investigated. The ZrO2 in contact with Pd was found to be reducible and to enhance the methane-oxidation.

A Au@TiO2/Si-Al2O3 catalyst was also synthesized and examined for CO oxidation. It was found that the strong interaction between Au and TiO2 not only enhanced the oxidation activity of Au but also effectively prevented Au sintering up to 873 K.

Additionally, catalysts with Pd or Pt cores and ZnO shells were prepared. The formation of Pt-Zn alloy was suggested by in-situ TEM and coulometric titration results and by catalytic properties for methanol-steam-reforming.

Finally, metal-oxide interactions were compared for Pd@CeO2 and Pt@CeO2. A very strong interaction between Pd and CeO2 helped to stabilize the core-shell structure at higher calcination temperatures and affected the CO accessibility of the core for catalyst calcined at lower temperatures, but these were not observed with Pt.

Files over 3MB may be slow to open. For best results, right-click and select "save as..."

Share

COinS