| The design of high-yield, selective catalysts for the reforming and conversion of hydrocarbon feedstocks into fuels, value-added chemicals, materials, and other products is an important goal in heterogeneous catalysis. A successful hydrocarbon reforming and conversion catalyst must be one that selectively cleaves the strong C-H and C-C bonds of the inherently stable alkane and cycloalkane molecules that are used as feed streams in these industrial processes. While these catalytic hydrocarbon reactions have been performed rather extensively in industry for the past half-century, higher yields and selectivities for these processes are still realizable. Ultimately, the design and discovery of the best catalysts for these processes will require a detailed, fundamental understanding of these reactions at the microscopic level. Previous alkane activation experiments on single-crystalline transition metal surfaces have provided important fundamental information about initial C-H and C-C bond cleavage reactions of linear alkanes. In this work, the fundamental issues associated with initial, rate limiting C-H and C-C bond activation of cycloalkanes by catalytically active iridium and ruthenium single-crystalline surfaces will be identified and addressed by two different types of reactions. One of these reaction types, trapping-mediated dissociative chemisorption of cycloalkanes, enables quantitative measurement of the intrinsic reactivities of transition metal catalysts towards initial cycloalkane C-H and C-C bond cleavage. The data presented here for these trapping-mediated reactions will address many fundamental issues such as the influence of ring strain on the activation barrier for ring-opening C-C bond cleavage, the influence of molecular geometry on the activation barrier for C-H bond cleavage, and the affect of different transition metals on cycloalkane reaction mechanisms and kinetics. The other reaction type, multilayer-induced reaction of cyclobutane, provides quantitative insight into reactions occurring at the liquid-solid interface since this reaction occurs at the surface due to the presence of a condensed multilayer. Multilayer-induced reaction, reported here for the first time, has the potential of providing significant mechanistic and kinetic information about reactions that occur at the liquid-solid interface. The cycloalkane activation data presented in this dissertation provide significant new insight into the reactions of alkanes with transition metal catalysts. |
