Hydrogen: "More than just a reactant"

STACCHIOLA, DARIO J.; CALAZA, FLORENCIA C.; TYSOE, WILFRED T.

Philadelphia, PA

Conferencia; 228th ACS National Meeting; 2004

American Chemical Society

To study the effect of hydrogen on hydrogenation reactions, the adsorption of ethylene on a hydrogen pre-covered Pd(111) surface was studied by reflection absorption spectroscopy (RAIRS). The effect of either surface or subsurface hydrogen on the state of ethylene hybridization was studied by making use of the order-disorder transition of hydrogen on Pd(111)at low temperatures, during which the proportion of surface and subsurface hydrogen varies. The results indicate that subsurface hydrogen is responsible for the formation of pi-bonded ethylene on hydrogen-covered Pd(111). Another reaction that has been extensively studied is the formation of benzene from acetylene. Under reaction conditions, the reaction is poisoned by the formation of a crowded vinylidene layer, but the addition of hydrogen enhances the rate of benzene formation. Under this conditions, hydrogen transforms the surface layer to a more open surface form by ethylidyne.