title: Oxygen vacancy-assisted coupling and enolization of acetaldehyde on CeO2(111).
abstract: The temperature-dependent adsorption and reaction of acetaldehyde (CH(3)CHO) on a fully oxidized and a highly reduced thin-film CeO(2)(111) surface have been investigated using a combination of reflection-absorption infrared spectroscopy (RAIRS) and periodic density functional theory (DFT+U) calculations. On the fully oxidized surface, acetaldehyde adsorbs weakly through its carbonyl O interacting with a lattice Ce(4+) cation in the η(1)-O configuration. This state desorbs at 210 K without reaction. On the highly reduced surface, new vibrational signatures appear below 220 K. They are identified by RAIRS and DFT as a dimer state formed from the coupling of the carbonyl O and the acyl C of two acetaldehyde molecules. This dimer state remains up to 400 K before decomposing to produce another distinct set of vibrational signatures, which are identified as the enolate form of acetaldehyde (CH(2)CHO¯). Furthermore, the calculated activation barriers for the coupling of acetaldehyde, the decomposition of the dimer state, and the recombinative desorption of enolate and H as acetaldehyde are in good agreement with previously reported TPD results for acetaldehyde adsorbed on reduced CeO(2)(111) [Chen et al. J. Phys. Chem. C 2011, 115, 3385]. The present findings demonstrate that surface oxygen vacancies alter the reactivity of the CeO(2)(111) surface and play a crucial role in stabilizing and activating acetaldehyde for coupling reactions.
authors.affiliation: Chemical Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA.
authors.forename: Florencia C
authors.initials: FC
authors.lastname: Calaza
authors.forename: Ye
authors.initials: Y
authors.lastname: Xu
authors.forename: David R
authors.initials: DR
authors.lastname: Mullins
authors.forename: Steven H
authors.initials: SH
authors.lastname: Overbury
mesh_terms: D000079:Acetaldehyde / Q000737:chemistry*; D000327:Adsorption; D002563:Cerium / Q000737:chemistry*; D010100:Oxygen / Q000737:chemistry*; D010316:Particle Size; D011789:Quantum Theory; D013055:Spectrophotometry, Infrared; D013499:Surface Properties; D013696:Temperature
chemical_list: D002563:Cerium; C030583:ceric oxide; D000079:Acetaldehyde; D010100:Oxygen