Experimental Modeling of Heterogeneous Catalysis Using Gold-based Surfaces

Abstract

This thesis investigates fundamental principles that guide elementary reactions on the surface of heterogeneous catalysts. Experimental modeling using gold single crystal surfaces and gold-based bimetallic surface alloys under ultra-high vacuum environments provided insights into the kinetics of elementary reactions, solvation of reactive intermediates and effects of dilute secondary metals. First, the experimental determination and computation using density functional theory of the rate constant parameters for formate decomposition on coinage metal surfaces are discussed (Chapter 1). The study provides insight into the underlying factors that result in the relatively high pre-exponential factors for unimolecular decomposition on metal surfaces and difficulties and suggestions for accurate prediction of rate constants for elementary reaction steps on metal surfaces. Second, the interactions between adsorbed reaction intermediates and coadsorbed, intact molecules on the gold surface are described. The adsorption of intact methanol molecules on Au(110) is shown to be stabilized by surface-bound methoxy species (Chapter 2). Water molecules also hydrate surface-bound acetate and desorb at significantly higher temperatures compared to desorption from the clean Au(110) surface (Chapter 3). Inclusion of these interactions in kinetic models may be necessary for accurate microkinetic analysis of the rates and selectivities of catalytic reactions in both the gas and liquid phases whenever appreciable coverages of species from the ambient phase exist. Third, the effects of dilute metals in gold are explored through preparation, characterization and reactivity studies of gold-based bimetallic surfaces. Rhenium and manganese are deposited from dimetal decacarbonyls by selective removal of the CO ligands using low energy electrons (Chapter 4). The reactivity towards deuterium and hydrogen of the resultant ReAu and MnAu surfaces are described. Our results provide information that may be useful for developing active and selective catalysts that take advantage of rhenium’s ability to dissociate strong bonds. Lastly, discussed in appendices are unpublished results on the kinetics of alcohol desorption from Au(110) (Chapter 5), reactivity of pure Pd(111) surface towards alcohols and C3 species (Chapter 6) as well as characterization and reactivity study of PdAu(111) surface (Chapter 7).