Ethylene Adsorption on Clean and Oxygen Covered Flat and Stepped Ag(001)

Abstract

In the present paper we review our findings on ethylene adsorption on clean and oxygen covered Ag(001) surfaces investigated by dosing the gas with a Supersonic Molecular Beam and analysing the adsorption state either by High Resolution Electron Energy Loss Spectroscopy or by High Resolution X Rays Photoemission Spectroscopy. The final adsorption state depends on the translational and on the internal energy of the gas-phase molecules and on the presence of defects. At low translational energy ethylene either physisorbs or very weakly chemisorbs at flat terrace sites. The physisorption probability is thereby hindered by rotational excitation. A more strongly bound, π bonded, state forms at higher translational energy, the activation barrier being related to the energy needed to form the relevant defect at which chemisorption takes place. A further even more strongly bound state forms only when dosing vibrationally excited molecules from the gas phase.

Coverage dependence of the dynamics of ethylene adsorption on Ag(210)

“…Ethylene adsorption at Ag surfaces [3,4] is particularly important for the understanding of the so-far unsolved ethylene epoxidation reaction [5][6][7][8] for which surface defects might play a pivotal role. This paper follows our previous investigations of C 2 H 4 adsorption on Ag(100) and Ag(410) [9][10][11][12][13][14][15]. In these experiments we demonstrated that physisorbed and π-bonded states exist on Ag(100) and are characterized by a different adsorption energy [9] and by a different C 1s photoemission signature [11].…”

“…A less strongly bound moiety, metastable at the temperature of the experiment, appears only at higher coverage. Preliminary data on the C 2 H 4 interaction with Ag(210) were reported briefly in previous papers [14,15] and are completed by the present, detailed, report on energy, angle and coverage dependence of the sticking probability.…”

Ethene stabilization on Cu(111) by surface roughness

“…7 0.08 ML of Br/Cl was thereby found to shift the ethene desorption peak in TPD to 132 K. A stabilization of ethene adsorption at undercoordinated atoms was found also at Ag surfaces, possibly providing a mechanism for the relatively high desorption temperatures observed experimentally ͑about 140 K͒. 28,40,43 The stabilization of ethene on less defined rough copper surfaces was previously reported by thermal desorption spectroscopy by Otto and co-workers 30,31 who found a broad desorption peak of ethene at around 210 K in agreement with our findings. Their spectra also show that the wagging mode 7 / 8 remains nearly unshifted compared to ethene on Cu͑111͒, as indicated in Table I.…”

Bridging the structure gap: Chemistry of nanostructured surfaces at well-defined defects

“…A further point to be clarified is the role of oxygen in stabilizing and promoting ethylene adsorption on Ag(100) ( [424] and references therein). The desorption temperature of ethylene on Ag (100) in presence of oxygen is close to the one measured on bare stepped Ag surfaces, i.e.…”