Reaction Thermodynamics of Hydrocarbons with Ni(100)

The reactions of simple hydrocarbons with a Ni(100) surface were studied by temperature-programmed reaction and Auger electron spectroscopy. All the hydrocarbons were found to desorb molecularly below a critical temperature dependent on the hydrocarbon. Above the critical temperature dehydrogenation /decomposition reactions occur. Simple alkenes, ethene, propene, butene, and benzene, all decomposed to adsorbed hydrogen and carbon above this critical temperature. Cyclohexene was found to dehydrogenate to benzene circa 200 K. Butadiene was hydrogenated to butenes circa 270 K. Many of these findings are predicted by simple thermodynamic analysis of the Ni-hydrocarbon-hydrogen system. Thermodynamic analysis also predicts that a variety of hydrogenation and hydrogenolysis reactions are feasible, and these reactions were not observed. The comparison of thermodynamic predictions with experimental findings suggests C-H bond activation of unsaturated hydrocarbons on Ni is facile but the hydrogenation of alkyl intermediates to alkanes is difficult. The results also suggest C-C bond activation is difficult on Ni(100).