PATHWAYS FOR CARBOXYLIC-ACID DECOMPOSITION ON TIO2
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The decomposition reactions of formic, acetic, and propionic acids were studied on TiO2(anatase) by using temperature-programmed desorption. Two adsorbed phases were observed following carboxylic acid adsorption at room temperature: molecular carboxylic acids and carboxylates. While the molecular species adsorbed reversibly, the surface carboxylates desorbed via two different pathways: recombination with the surface hydroxyl species at 400 K and decomposition at higher temperatures. Less than 40% of the total carboxylate coverage was removed from the surface as the parent carboxylic acid via the recombination pathway. The peak temperatures for carboxylate decomposition were in the order formate (525 K) < propionate (595 K) < acetate (615 K). A unimolecular dehydration reaction was common to each of the carboxylates studied: CO, ketene, and acrolein were produced from formate, acetate, and propionate, respectively. While formate decomposed exclusively via unimolecular dehydration, acetate and propionate decomposed selectively to dialkyl ketones plus CO2via a bimolecular ketonization pathway. 1988, American Chemical Society. All rights reserved.