An atomic level understanding of the structure and stability of model catalysts is
essential for surface science studies in heterogeneous catalysis. Scanning tunneling
microscopy (STM) can operate both in UHV and under realistic pressure conditions with
a wide temperature span while providing atomic resolution images. Taking advantage of
the ability of STM, our research focuses on 1) investigating the structure and stability of
supported Au catalysts, especially under CO oxidation conditions, and 2) synthesizing
and characterizing a series of alloy model catalysts for future model catalytic studies.
In our study, Au clusters supported on TiO2(110) have been used to model
supported Au catalysts. Our STM studies in UHV reveal surface structures of TiO2(110)
and show undercoordinated Ti cations play a critical role in the nucleation and
stabilization of Au clusters on TiO2(110). Exposing the TiO2(110) surface to water vapor
causes the formation of surface hydroxyl groups and subsequently alters the growth
kinetics of Au clusters on TiO2(110). STM studies on Au/TiO2(110) during CO
oxidation demonstrate the real surface of a working catalyst. Au clusters supported on TiO2(110) sinter rapidly during CO oxidation, but are mostly stable in the single
component reactant gas, either CO or O2. The sintering kinetics of supported Au clusters
has been measured during CO oxidation and gives an activation energy, which supports
the mechanism of CO oxidation induced sintering. CO oxidation was also found to
accelerate the surface diffusion of Rh(110). Our results show a direct correlation
between the reaction rate of CO oxidation and the diffusion rate of surface metal atoms.
Synthesis of alloy model catalysts have also been attempted in our study with
their structures successfully characterized. Planar Au-Pd alloy films has been prepared
on a Rh(100) surface with surface Au and Pd atoms distinguished by STM. The growth
of Au-Ag alloy clusters have been studied by in-situ STM on a cluster-to-cluster basis.
Moreover, the atomic structure of a solution-prepared Ru3Sn3 cluster has been resolved
on an ultra-thin silica film surface. The atomic structure and adsorption sites of the ultrathin
silica film have also been well characterized in our study.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/ETD-TAMU-3269 |
| Date | 15 May 2009 |
| Creators | Yang, Fan |
| Contributors | Goodman, D. Wayne |
| Source Sets | Texas A and M University |
| Language | en_US |
| Detected Language | English |
| Type | Book, Thesis, Electronic Dissertation, text |
| Format | electronic, application/pdf, born digital |
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