Abstract
The adsorption and decomposition of ethene on the Fe(111) surface has been investigated using a molecular beam reactor and XPS. These data show that ethene is decomposed fully to atomic carbon and gas phase hydrogen at all the substrate temperatures considered (373–873K). There is a transition from saturation behaviour (that is, termination of adsorption after the uptake of 0.3–0.45 monolayers of ethene) below 575K to continued steady-state uptake of ethene above that temperature. This is due to fast diffusion of carbon deposited on the surface into the subsurface region, which always leaves free surface sites for ethene adsorption and decomposition. In going from 373 to 873K the initial sticking probability drops from 0.4 to 0.12, but above 723 the initial sticking probability is maintained, even after 1.63–1.94 monolayers of carbon had already been adsorbed. The deposited carbon can be removed at high rate with oxygen above ∼600K; the carbon is evolved as CO, with no evidence of CO2 production, due to the short lifetime of molecular CO on the surface at those temperatures.
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