HYDROCARBON SURFACE CHEMISTRY OF PLATINUM AND NICKEL

The hydrocarbon surface chemistry of Pt and Ni as related to heterogeneous catalysis was pursued in this thesis research. The key issue was to delineate the electronic, compositional and stereochemical features and reaction mechanisms of hydrocarbon adsorbates that facilitate the scission and formation of C-H and C-C bonds. These studies were performed under ultra high vacuum conditions, over a series of crystallographic planes of Pt and Ni.;The coordination chemistry of benzene, toluene and pyridine on flat and stepped Pt and Ni surfaces has been defined by chemical displacement reactions, thermal desorption spectroscopy and isotopic labeling studies. Important electronic and stereochemical features of C-H bond breaking and making processes for aromatic hydrocarbons were identified, and distinctive differences between Pt and Ni surfaces were established from this study.;Reactions of cyclic hydrocarbons on flat and stepped Ni and Pt surfaces were investigated using the same approach as for the aromatic hydrocarbons. Dehydrogenation of cyclohexane, cyclohexene and 1,3- and 1,4-cyclohexadiene to form benzene was studied as a function of metal surface, surface crystallography and composition. H-D exchange reactions during dehydrogenation, resulting in all possible mixed benzene species, were evident on all the Pt surfaces studied. Dehydrogenation of C(,8) cyclic olefins also led to the formation of delocalized ring species--cyclooctatetraene on a Pt surface. Using selectively labeled molecules, the reaction mechanism for cycloheptatriene conversion to benzene on Ni(100), and for norbornadiene conversion to benzene on Pt(111) and Pt(100) have been incisively studied.;Reactions of acetylene and hydrogen on Pt(111) and Pt(100) investigated using primarily thermal desorption spectroscopy and isotopic labeling techniques. Distinguishing features of C-H bond breaking and forming between acetylene and hydrogen as a function of surface crystallography, temperature and pressure were established.