TPD and HREELS reinvestigation of ethylene oxide adsorption on Pt(1 1 1)

A reinvestigation of ethylene oxide (EtO) adsorption and desorption on Pt(1 1 1) is reported using primarily TPD, AES, XPS and HREELS. EtO does not react when adsorbed on Pt(1 1 1) at 90 K and then subsequently heated under UHV conditions. Specifically, TPD results and AES measurements taken after TPD experiments place an upper limit on the extent of EtO decomposition at 0.02 ML. This work helps to correct earlier work that showed significant decomposition on this surface. HREELS identified molecular EtO adsorption at 90 K, with only small shifts in molecular vibrational frequencies from condensed phase spectra. At a coverage of less than 0.1-ML EtO, EtO is bonded oxygen-end down to the Pt(1 1 1) surface with C_2v symmetry, i.e., with the C₂ axis of EtO normal to the surface. By showing that the close-packed Pt(1 1 1) surface is less reactive toward the desired product of ethylene epoxidation than previously thought, these new results should be helpful in discussing differences between the chemistry of Ag and Pt catalysts for this reaction.