Fundamental Studies of Catalytic Dehydrogenation on Alumina-supported Size-selected Platinum Cluster Model Catalysts

Abstract

The research presented in this dissertation focuses on the use of platinum-based catalysts to enhance endothermic fuel cooling. Chapter 1 gives a brief introduction to the motivation for this work. Chapter 2 presents fundamental studies on the catalytic dehydrogenation of ethylene by size-selected Ptn (n = 4, 7, 8) clusters deposited onto thin film alumina supports. The model catalysts were probed by a combination of experimental and theoretical techniques including; temperature-programmed desorption and reaction (TPD/R), low energy ion scattering spectroscopy (ISS), X-ray photoelectron spectroscopy (XPS), plane wave density-functional theory (PW-DFT), and statistical mechanical theory. It is shown that the Pt clusters dehydrogenated approximately half of the initially adsorbed ethylene, leading to deactivation of the catalyst via (coking) carbon deposition. The catalytic activity was observed to be size-dependent and strongly correlated to the cluster structure, with Pt7 demonstrating the highest activity. In Chapter 3 the focus turns to selectively doping Pt7 clusters with boron. A combination of experiment and theory were used investigate the alkene-binding affinity of the bimetallic (PtnBm/alumina) model catalysts. A comparison of the theoretical and experimental results show that doping the Pt clusters with boron modifies the alkene-binding affinity and thus the tendency toward dehydrogenation to coke precursors. Chapter 4 describes a way to produce bimetallic (PtnBm/alumina) model catalysts by exposing prepared Ptn/alumina samples to diborane and heating. It is shown that the diborane exposure/hearting procedure results in the preferential binding of B to the Pt clusters.