Oxygen storage in reducible oxides studied by ultra-thin film growth on single-crystal oxide substrates / Ernisse Steve Putna.

Format:

Book

Manuscript

Microformat

Thesis/Dissertation

Author/Creator:

Putna, Ernisse Steve.

Contributor:

Gorte, Raymond J., advisor.

University of Pennsylvania.

Language:

English

Subjects (All):

Penn dissertations--Chemical engineering.

Chemical engineering--Penn dissertations.

Local Subjects:

Penn dissertations--Chemical engineering.

Chemical engineering--Penn dissertations.

Physical Description:

xvii, 187 pages ; 29 cm

Production:

1998.

Summary:

Thermal desorption and steady-state CO oxidation measurements were performed on model catalysts to gain a better understanding of the redox properties of oxygen-storage components in three-way, automotive-emissions-control catalysts. The interactions of these components with group VIII metals, and the effect of those interactions on catalytic properties, was also examined.

Thermal desorption of O$\sb2$ was used to probe directly the oxidation and reduction of ceria, the primary oxygen-storage component used in emissions-control catalysts. For the first time, it was shown that there is a weakly bound form of lattice oxygen on small ceria crystallites, not found on inactive forms of ceria, and that this species of oxygen results in the enhanced CO oxidation activity of ceria-supported metals. Furthermore, interactions with zirconia, which is known to promote ceria in commercial catalysts, were found to greatly increase the fraction of weakly bound oxygen on ceria, as well as the CO oxidation activity. Metal-support interactions, unique to single-crystalline ceria and Rh, were found to promote unusually high CO dissociation activity. Insights gained from these measurements were used to design a novel, ceria-based anode for a solid-oxide fuel cell which could oxidize methane directly, with performance comparable to that obtained using hydrogen.

In addition to ceria, the catalytic properties of other reducible oxides, praseodymia and lanthana, were examined to determine the potential of these oxides as oxygen-storage components. While it was determined that praseodymia likely cannot be utilized in its pure form due to slow reoxidation, the results provided further insights into why ceria-based mixed oxides are such effective oxygen-storage components. While lanthana is normally considered to be non-reducible, lanthana could be reduced in CO and could promote the steady-state reduction of NO by CO. However, like ceria, the ability of lanthana to promote redox chemistry is dependent on its structure.

Finally, the interaction of oxygen with Rh, Pt, and Pd was studied as a function of particle size. Desorption from Pt and Pd was found to be strongly structure sensitive, whereas desorption from Rh was roughly independent of particle size.

Notes:

Adviser: Raymond J. Gorte.

Thesis (Ph.D. in Chemical Engineering) -- University of Pennsylvania, 1998.

Includes bibliographical references.

Local Notes:

University Microfilms order no.: 98-40227.

OCLC:

187472979