Fast x-ray spectroscopy study of ethene on clean and SO₄ precovered Pt{111}

The adsorption and decomposition of ethylene over a Pt{111} single crystalsurface has been investigated by fast x-ray spectroscopy. At 100 K ethene displays precursor-mediated adsorption kinetics, adopting a single environment with a saturation C₂H₄ coverage of 0.25 ML and binding energy of 283.2 eV. Thermal decomposition proceeds above 240 K via dehydrogenation to ethylidyne with an activation barrier of 57±3 kJ mol⁻¹ and preexponential factor ν=1×10^10±0.5 s⁻¹. Site-blocking by preadsorbed SO₄ reduces the saturation ethene coverage but induces a new, less reactive π-bonded ethene species centered around 283.9 eV, which in turn decomposes to ethylidyne at 350 K.