Oxygen vacancy-promoted coupling and formation of enolate for acetaldehyde on CeO2(111) surfaces

XU, YE; CALAZA, FLORENCIA C.; MULLINS, DAVID R.; OVERBURY, STEVEN H.

New Orleans

Conferencia; 245th ACS National Meeting; 2013

AMERICAN CHEMICAL SOCIETY

Enolate species are the key intermediates in several organic C-C coupling reactions including aldol condensation, which are important pathways in the conversion of biomass-derived feedstock to fuels and chemicals. We used a combination of RAIRS and DFT calculations to demonstrate that oxygen vacancies on CeO2(111) are key to activate acetaldehyde and stabilize it in the enolate form (CH2CHO). Acetaldehyde desorbs without reaction from the stoichiometric CeO2(111) surface around 210 K. When the surface is partially reduced, acetaldehyde loses its carbonyl bond character at low temperatures. Annealing to 400 K leads to the desorption of some of the strongly adsorbed species as acetaldehyde and the appearance of another organic species, conclusively identified to be the enolate on the basis of the IR signatures, previous X-ray results, and DFT calculations. A reaction energy profile is constructed based on the surface intermediates on CeO2-x(111), which finds good agreement with previous TPD results.