(544dv) Density Functional Theory Study of Decarboxylation and Decarbonylation of Acetic Acid over Pd (111)

The study of acetic acid (CH₃COOH) decomposition over Pd (111) surface is a good model system to study decomposition of acids and oxygenates, which are common in biomass conversion. Understanding the reaction mechanism of acetic acid decomposition, at an atomic scale, will help us design more effective catalyst and catalyst system. Here we present Density Functional Theory calculations of the elementary steps involved in the decomposition of acetic acid on Pd (111). We investigated the reaction mechanism for both decarboxylation and decarbonylation of acetic acid and our results suggest that the major pathway for decarbonylation proceed through dehydrogenation of acetic acid(CH₃COOH) to acetate(CH₃COO), followed by α-carbon dehydrogenation of the acetate to carboxylmethylidene(CH₂COO). This follows by α-carbon dehydrogenation of the CH₂COO to carboxylmethylidyne(CHCOO) and CH-COO bond scission to form CH and CO_2. The decarboxylation pathway proceeds via dehydrogenation of acetic acid(CH₃COOH) to acetate(CH₃COO), followed by α-carbon dehydrogenation of the acetate to carboxylmethylidene(CH₂COO), followed by deoxygenation of the CH₂COO to ketene(CH₂CO). This follows by α-carbon dehydrogenation of CH₂CO to ketyne (CHCO), and finally CH-CO bond scission to yield CH and CO. Consequently, the competition between the decarbonylation and decarboxylation pathway depends on the deoxygenation of CH₂COO to CH₂CO and dehydrogenation of the CH₂COO to CHCOO.