Abstract
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•Overview of ketonization of carboxylic acids, aldehydes, alcohols, and esters.•Acid, aldehyde, alcohol, and ester ketonization pathways are closely related.•Ketonization depends on catalyst redox and acid-base properties and pretreatment.•Additional kinetic, spectroscopic, and computational studies further required.
The ketonization of various renewable biomass-derived oxygenated feedstocks such as carboxylic acids, aldehydes, alcohols, and esters is presented. As most previous ketonization reports focused on carboxylic acids, this overview extends the scope to homo-, cross-, and cyclo-ketonization of not only carboxylic acids (e.g., acetic, propionic, butyric, lactic, valeric, levulinic, dicarboxylic, and higher acids), but also of lesser reported aldehydes (e.g., acetaldehyde, propionaldehyde, and butyraldehyde), alcohols (e.g., ethanol, propanol, butanol, diols, and higher alcohols), and esters (e.g., small, intermediate, and large alkanoate chain length esters) aiming at obtaining more stable products, biofuels, and high-value chemicals. Ketonization of carboxylic acids (e.g., catalysts, mechanisms) is presented to provide the basis for understanding the ketonization of aldehydes, alcohols, and esters over metal oxides including ceria, titania, and zirconia, which have been the most active and studied catalysts for this reaction. Whenever possible, examples of ketonization of biomass-derived oxygenated compounds are presented to highlight the utility of the reaction and its practical application. As biomass product streams can contain a large number of different oxygenated compounds (e.g., more than 350 compounds in bio-oil), ketonization examples in the presence of more than one oxygenated molecule have also been considered.