Abstract
Using a combination of two surface-sensitive spectroscopy techniques, the chemical state of the Ag(111) surface and the nature of the adsorbed species in the presence of ethylene and oxygen gases are identified. In the 10 mbar pressure range and 25–200 °C studied here, Ag(111) remains largely metallic even in O2-rich conditions. The only adsorbed molecular species with a low but discernible coverage is surface carbonate, which forms due to further oxidation of produced CO2, in a similar manner to its formation in ambient air on Ag surfaces. Its formation is also pressure-dependent, for instance, it is not observed when the total pressure is in the 1 mbar pressure range. Production of carbonate, along with carbon dioxide and water vapor as the main gas-phase products, suggests that an unpromoted Ag(111) surface catalyzes mainly the undesired full oxidation reaction.
Highlights
Ethylene oxide (EtO) is a key raw material for ethylene glycol production, which is the main component in antifreeze and a precursor for polyesters and polyurethanes [1].EtO is used as a sterilizer and a disinfectant [1]
In traditional surface science studies performed under ultra-high vacuum (UHV) conditions, there was a great deal of interest in the O/Ag system because various types of adsorbed oxygen species, oxygen-induced surface reconstructions, and oxides can form depending on the conditions
Using PM-IRRAS, we found that the only molecular species on the surface is carbonate, which is present in the 10 mbar pressure range, and below a certain temperature that depends on the partial pressure of Et and O2
Summary
Ethylene oxide (EtO) is a key raw material for ethylene glycol production, which is the main component in antifreeze and a precursor for polyesters and polyurethanes [1].EtO is used as a sterilizer and a disinfectant [1]. More relevant for heterogeneous catalysis are the studies that were performed at room temperature (RT) and above, and in the presence of O2 with the goal of identifying various types of oxygen that can be present on the surface and how they play a role in catalyst’s performance [5,6,7,8,9,10,11,12] According to these studies, the two most important oxygen species have different binding energies (BE) in an x-ray photoelectron spectroscopy (XPS) spectrum: a peak at 528.1–528.4 eV that
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