Journal
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
Volume 134, Issue 43, Pages 18034-18045Publisher
AMER CHEMICAL SOC
DOI: 10.1021/ja3074243
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Funding
- Division of Chemical Sciences, Geosciences, and Biosciences, Office of Basic Energy Sciences, U.S. Department of Energy at Oak Ridge National Laboratory (ORNL) [DE-AC05-00OR22725]
- Oak Ridge Institute for Science and Education
- ORNL
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The temperature-dependent adsorption and reaction of acetaldehyde (CH3CHO) on a fully oxidized and a highly reduced thin-film CeO2(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 Ce4+ cation in the eta(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 (CH2CHO-). 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 CeO2(111) [Chen et al. J. Phys. Chem. C 2011, 115, 3385]. The present findings demonstrate that surface oxygen vacancies alter the reactivity of the CeO2(111) surface and play a crucial role in stabilizing and activating acetaldehyde for coupling reactions.
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