(448a) Mechanistic Study on C-C Coupling of Acetaldehyde on Partially Reduced CeO2-X(111)

Selective C-C coupling catalyzed by solid catalysts is pertinent to the manufacture of fuel and chemical products from renewable or available carbon sources such as biomass and C1 compounds including methane and CO₂. A versatile way to accomplish C-C coupling between organic oxygenates is aldol addition/condensation. Here we use density functional theory calculations and microkinetic modeling to gain fundamental insights into how ceria, an earth-abundant solid material, catalyzes C-C coupling reactions at the molecular level, with acetaldehyde (AcH) as a representative carbonyl compound. We show how an enolate-based mechanism is capable of explaining the main features of temperature programmed desorption of AcH on CeO₂(111)¹ and how it suggests AcH might be coaxed into undergoing C-C coupling to form crotonaldehyde under UHV conditions, which is experimentally confirmed. We then extend the UHV mechanisms to account for finite pressure effects and compare the expanded version with one proposed by Mann et al.² Important features of our proposed reaction mechanisms^3,4 include oxygen vacancy-catalyzed enolization of AcH, surface-mediated intermolecular H transfer, and dynamic behavior of oxygen vacancies, which may be generally relevant to organic reactions on reducible oxides.

1. L. Chen, D.R. Mullins, J. Phys. Chem. C 2011, 115, 3385.
2. K.P. Mann, Z. Wu, F.C. Calaza, S.H. Overbury, ACS Catal. 2014, 4, 2437.
3. C. Calaza, Y. Xu, D.R. Mullins, S.H. Overbury, J. Am. Chem. Soc. 2012, 134, 18034.
4. Zhao C, Y. Xu, Top. Catal. 2017, 60, 446.