| dc.description.abstract | This dissertation is focused on understanding the structure-activity relationship in
heterogeneous catalysis by studying model catalytic systems.
The catalytic oxidation of CO was chosen as a model reaction for studies on a
variety of catalysts. A series of Au/TiO2 catalysts were prepared from various metalorganic
gold complexes. The catalytic activity and the particle size of the gold catalysts
were strongly dependent on the gold complexes. The Au/TiO2 catalyst prepared from a
tetranuclear gold complex showed the best performance for CO oxidation, and the
average gold particle size of this catalyst was 3.1 nm. CO oxidation was also studied
over Au/MgO catalysts, where the MgO supports were annealed to various temperatures
between 900 and 1300 K prior to deposition of Au. A correlation was found between the
activity of Au clusters for the catalytic oxidation of CO and the F-center concentration in
the MgO support.
In addition, the catalytic oxidation of CO was studied in a batch reactor over
supported Pd/Al2O3 catalysts, a Pd(100) single crystal, as well as polycrystalline metals
of rhodium, palladium, and platinum. A hyperactive state, corresponding to an oxygen covered surface, was observed at high O2/CO ratios at elevated pressures. The reaction
rate at this state was significantly higher than that on CO-covered surfaces at
stoichiometric conditions. The oxygen chemical potential required to achieve the
hyperactive state depends on the intrinsic properties of the metal, the particle size, and
the reaction temperature.
A well-ordered ultra-thin titanium oxide film was synthesized on the Mo(112)
surface as a model catalyst support. Two methods were used to prepare this Mo(112)-
(8x2)-TiOx film, including direct growth on Mo(112) and indirect growth by deposition
of Ti onto monolayer SiO2/Mo(112). The latter method was more reproducible with
respect to film quality as determined by low-energy electron diffraction and scanning
tunneling microscopy. The thickness of this TiOx film was one monolayer and the
oxidation state of Ti was +3 as determined by Auger spectroscopy, high-resolution
electron energy loss spectroscopy, and X-ray photoelectron spectroscopy. | en |
