The adsorption of ethylene on Au/Pd(1 1 1) alloy surfaces

• Published in: Surface science 2007-02, Vol.601 (3), p.714-722
• Main Authors: Calaza, F., Gao, F., Li, Z., Tysoe, W.T.
• Format: Article
• Language: English
• Subjects: Chemisorption; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Condensed matter: structure, mechanical and thermal properties; Cross-disciplinary physics: materials science; rheology; Ethylene; Exact sciences and technology; Infrared absorption spectroscopy; Palladium gold alloy; Physics
• ISSN: 0039-6028; 1879-2758
• DOI: 10.1016/j.susc.2006.10.039

The adsorption of ethylene on gold–palladium alloys formed on a Pd(1 1 1) 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(1 1 1) 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 π-bonded configuration (with a σ–π 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(1 1 1). A corresponding increase in the σ–π parameter is also found as the gold coverage decreases reaching a value of ∼0.8, assigned to di-σ-bonded ethylene as found on clean Pd(1 1 1).