Nanoscience and Microsystems ETDs

Author

John Jones

Publication Date

2-1-2016

Abstract

Supported platinum catalysts are used in the automotive industry for the oxidation of CO, hydrocarbons, and NOx. Dispersed Pt provides active sites for these reactions to occur. During the use of these catalyst, high temperatures will cause Pt to become volatile and sinter, forming large particles which will lead to a loss of catalytic activity. The study of Pt sintering has been of high priority for the automotive industry along with mechanisms that will reduce the effect of sintering. Developing an understanding of how supports can hinder sintering of Pt will lead to the preparation of more robust catalysts. A promising support for Pt is CeO2. Altering the synthesis of CeO2 can allow for different nanoshapes to be formed which lead to different surface facets being exposed. The three types of nanoshaped CeO2 synthesized for the catalyst are polyhedra, rods, and cubes, which expose different surface facets. The polyhedra produced expose primarily the (111) and (100) facet while rods expose (111) and cubes expose the (100). These three CeO2 nanoshapes will be tested to discover if one surface facet is able to trap Pt in a dispersed form after aging at high temperature. Powder catalysts containing CeO2 were produced to simulate diesel oxidation catalysts. A first set of catalysts was prepared using an incipient wetness technique of La-Al2O3 with chloroplatinic acid producing Pt/La-Al2O3. This product was then mixed with each of the CeO2 nanoshapes and aged at 800 °C. The resulting products were analyzed to determine if the volatile Pt had sintered or had transferred from the La-Al2O3 support and become trapped on the CeO2 support. A second set of catalysts was prepared using an incipient wetness technique of each of the CeO2 nanoshapes with chloroplatinic acid, producing Pt/CeO2. These catalysts were then aged at 800 °C and analyzed to determine the effectiveness of the different exposed surface facets at keeping Pt in a dispersed phase. Dispersion of Pt after aging at high temperature was shown to have been greatly affected by the type of CeO2 support used. In both parts of this research, it was found that the CeO2 cubes, exposing primarily the (100) facet, were not able to keep Pt highly dispersed, allowing for the growth of large Pt particles. The catalysts containing either the CeO2 polyhedra or rods, which exposed the (111) facet, were shown to trap Pt in an atomically dispersed state. This allowed for high catalytic reactivity to be maintained even after aging at high temperature.

Keywords

Platinum, Ceria, Sintering, Trapping, CO oxidation, TEM, X-ray diffraction, CeO2

Document Type

Thesis

Language

English

Degree Name

Nanoscience and Microsystems

Level of Degree

Masters

Department Name

Nanoscience and Microsystems

First Advisor

Datye, Abhaya

First Committee Member (Chair)

Datye, Abhaya

Second Committee Member

Challa, Sivakumar

Third Committee Member

Fernando, Garzon

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