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

The decomposition mechanisms of ethanol and ethylene glycol on well-ordered stoichiometric CeO2(111) and partially reduced CeO2-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 CO2 accompanied by desorption of acetaldehyde, H2O, and H-2. 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 CeO2-x (111) is favored with respect to C-O bond scission and yields methanol, formaldehyde, and CO accompanied by the desorption of H2O and H-2. Still, scission of C-O bonds on both sides of the ethylenedioxy species yields minor amounts of accompanying C2H4 and 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.