STRUCTURE-SENSITIVE DECOMPOSITION OF HYDROCARBONS ON NI(755)

Thermal decomposition of cycloparaffins (C6-C8) and normalparaffins (C5-C8) on a clean stepped Ni(755) surface was investigated by low-energy electron diffraction (LEED), Auger electron spectroscopy (AES) and temperature programmed desorption (TPD). All hydrocarbons were adsorbed on the surface at 123 K. No ordered LEED pattern was observed for all hydrocarbons at 123 K. All hydrocarbons decomposed partially on the surface and remained as surface carbon while heating up to 573 K. No other species than hydrogen and reactant hydrocarbons were observed during TPD measurement. The initial decomposition probabilities of the hydrocarbons depended on the desorption energies of the monolayer adsorption state of the hydrocarbons irrespective of the number of carbons of hydrocarbons and types of hydrocarbons, that is cyclo or normal. The decomposition activity was suppressed by pre-adsorbed carbon atoms at step sites. The step sites are active sites for the first step of decomposition of hydrocarbons and the reaction between hydrocarbons and step sites starts in a narrow temperature range.