The adsorption of ethylene on Au/Pd(111) alloy surfaces

The adsorption of ethylene on gold–palladium alloys formed on a Pd(111) surface is investigated using a combination of temperature-programmed desorption (TPD) and reflection absorption infrared spectroscopy (RAIRS). Various alloy compositions are obtained by depositing four monolayers of gold on a clean Pd(111) surface and annealing to various temperatures. For gold coverages greater than 0.7, ethylene adsorbs primarily on gold sites, desorbing with an activation energy of less than 55 kJ/mol. At gold coverages between 0.5 and 0.7, ethylene is detected on palladium sites in a p-bonded configuration (with a r–p parameter of 0.1) desorbing with an activation energy of between 57 and 62 kJ/mol. Further reducing the gold coverage leads to an almost linear increase in the desorption activation energy of ethylene with increasing palladium content until it eventually reaches a value of 76 kJ/mol found for ethylene on clean Pd(111). A corresponding increase in the r–p parameter is also found as the gold coverage decreases reaching a value of 0.8, assigned to di-r-bonded ethylene as found on clean Pd(111). 2006 Elsevier B.V. All rights reserved.