KINETIC AND REACTIVE PROPERTIES OF ETHYLENE ON CLEAN AND HYDROGEN-COVERED Pd(111)

Several molecular adsorption states are identified following ethylene adsorption on clean and hydrogen-covered Pd(111) using temperature-programmed desorption (TPD) and reflection absorption infrared spectroscopy (RAIRS). Di-σ-bonded ethylene forms on clean Pd(111) desorbing with an activation energy of 80 kJ/mol at low coverages. The strong intermolecular lateral interactions considerably reduce the desorption temperature at higher coverages. Π-bonded ethylene is formed on hydrogen-covered Pd(111), where the proportion of π-bonded species increases with hydrogen coverage. This species converts to the more stable di-σ-bonded species on heating. Ethane formation is detected in TPD from hydrogen-precovered Pd(111), which is predominantly formed by reaction with π-bonded ethylene.