Scanning tunneling microscopy studies on the structure and stability of model catalysts

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Title: Scanning tunneling microscopy studies on the structure and stability of model catalysts
Author: Yang, Fan
Abstract: 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 .
URI: http : / /hdl .handle .net /1969 .1 /ETD -TAMU -3269
Date: 2009-05-15

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Scanning tunneling microscopy studies on the structure and stability of model catalysts. Available electronically from http : / /hdl .handle .net /1969 .1 /ETD -TAMU -3269 .

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