The condensation of carboxylic acids is an important route to ketone production without toxic by-products. It serves to increase the carbon chain length while reducing the oxygen content of the molecules, which makes it also an attractive class of reaction for upgrading organic oxygenates derived from sustainable feedstock such as biomass or CO2. Ceria is known to be an active catalyst for ketonization of carboxylic acids, although a clear understanding of this ketonization activity remains elusive. Different mechanisms have been proposed to date, including the carboxylate mechanism, the acid anhydride mechanism, the ketene mechanism, and the β-ketoacid mechanism [1]. Temperature programmed desorption of acetic acid on CeO2(111) in UHV [2] contained several major features, including water desorption at 310 K and simultaneous water and ketene desorption at 590 K. Further increase in temperature led to the desorption of CO and CO2. IR spectroscopy suggested that at least two different acetate species coexist on CeO2(111) following water desorption at 310 K, which remain on the surface until ketene desorption [2]. Thus in UHV, a majority of surface acetates undergoes a dehydration pathway, while acetone is a minor product. In this talk, we present first-principles DFT calculations performed to elucidate the mechanism of the observed temperature programmed reactivity of acetic acid on CeO2(111). Our results indicate the ceria surface is reduced by the acidic protons at mild temperatures, leaving a mixture of surface acetate and oxygen vacancy-stabilized acetate. Oxygen vacancies play the critical role of facilitating eno-ization of acetate, which preferentially undergoes α-H abstraction to form an intermediate that is the precursor to both ketene desorption and acetone formation.

Theoretical investigation of the temperature-programmed reactivity of acetic acid on CeO2(111)

Where thousands of chemistry professionals meet to share ideas and advance scientific and technical knowledge. Spring 2023 abstracts, posters, and presentations will launch at the end of March.

ACS Spring 2023

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.