Microcalorimetric, infrared spectroscopic and DFT studies of ethylene adsorption on Ru, Ru/Sn and Ru/Cu catalysts

Microcalorimetric measurements of the adsorption of H₂, CO and C₂H₄ were conducted on silica-supported Ru, Ru/Sn, Ru/Cu and Cu catalysts; infrared spectroscopic measurements were made of adsorbed CO and C₂H₄. The adsorption of C₂H₄ leads to formation of di--adsorbed ethylene and ethylidyne species on Ru/SiO₂ at 300 K, with an initial heat of 160 kJ/mol. Ethylene adsorption at 203 K leads to the formation of di--adsorbed ethylene, ethylidyne species and weakly adsorbed -bonded ethylene. The initial heats are 110, 95 and 75 kJ/mol on Ru/SiO₂, 5Ru/Sn/SiO₂ and Ru/Cu/SiO₂, respectively. Lower heats of CO and C₂H₄ adsorption are measured on Ru/Cu/SiO₂, primarily as a result of these adsorbates binding on both Cu and Ru. Quantum chemical calculations employing density functional theory were performed using (0001) slabs of Ru and Ru/Sn. The results of these calculations indicate that Sn weakens the interaction of -bonded ethylene, di--bonded ethylene and ethylidyne species with Ru by 41, 23 and 15 kJ/mol, respectively. This behavior is in contrast to the effect of adding Sn to Pt and Pd, for which Sn preferentially weakens the bonding of ethylidyne species to the surface.