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

Microcalorimetric measurements of the adsorption of H-2, 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-sigma-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-sigma-adsorbed ethylene, ethylidyne species and weakly adsorbed pi-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 pi-bonded ethylene, di-sigma-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.