Redox-mediated C-C bond scission in alcohols adsorbed on CeO2 -xthin films

Abstract

The decomposition mechanisms of ethanol and ethylene glycol on well-ordered stoichiometric CeO₂(111) and partially reduced CeO_2-x(111) films were investigated by means of synchrotron radiation photoelectron spectroscopy, resonant photoemission spectroscopy, and temperature programmed desorption. Both alcohols partially deprotonate upon adsorption at 150 K and subsequent annealing yielding stable ethoxy and ethylenedioxy species. The C-C bond scission in both ethoxy and ethylenedioxy species on stoichiometric CeO₂(111) involves formation of acetaldehyde-like intermediates and yields CO and CO₂accompanied by desorption of acetaldehyde, H₂O, and H₂. This decomposition pathway leads to the formation of oxygen vacancies. In the presence of oxygen vacancies, C-O bond scission in ethoxy species yields C₂H₄. In contrast, C-C bond scission in ethylenedioxy species on the partially reduced CeO_2-x(111) is favored with respect to C-O bond scission and yields methanol, formaldehyde, and CO accompanied by the desorption of H₂O and H₂. Still, scission of C-O bonds on both sides of the ethylenedioxy species yields minor amounts of accompanying C₂H₄and C₂H₂. C-O bond scission is coupled with a partial recovery of the lattice oxygen in competition with its removal in the form of water.

Keywords: C–C bond scission; C–O bond scission; alcohols; cerium oxide; ethanol; ethylene glycol; vacancies.