PNNL

Abstract

The adsorption of the C2 hydrocarbons including ethane, ethene, and ethyne are studied on magnetite Fe3O4(001) by a combination of molecular beam dosing, temperature programmed desorption, and X-ray photoelectron spectroscopy. The ethane desorption profile has a single temperature invariant peak at 100 K while ethene and ethyne exhibit additional peaks at ~120 K and ~135 K. An inversion analysis is used to extract coverage dependent desorption energies as well as coverage-averaged prefactors for each molecule. Ethene and ethyne exhibit moderate coverage dependent desorption energies decreasing from ~80 to ~30 kJ/mol at saturation while ethane shows a relatively coverage invariant desorption energy ~28 kJ/mol. The desorption energies of the C2 hydrocarbons increase in order of increasing bond order. This is likely due to the enhanced interaction of the ethene and ethyne p system to the coordinatively unsaturated octahedral Fe sites (Feoct) on the ¬oxide surface. The saturation coverages of each C2 hydrocarbon at 82 K were also determined. These match well with the 2-dimensional spacing determined from their liquid densities. This work was supported by the US Department of Energy, Office of Science, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences & Biosciences and performed in EMSL, a national scientific user facility sponsored by the Department of Energy's Office of Biological and Environmental Research and located at Pacific Northwest National Laboratory (PNNL). PNNL is a multiprogram national laboratory operated for DOE by Battelle.