(530f) Theoretical Study of How Water Affects Acetic Acid Decomposition Using Density Functional Theory

Acetic acid decomposition on metal surfaces and the effects of water on the decomposition are good model systems for solvent effects on small oxygenates. Numerous studies have found that solvents influence the selectivity and rate of heterogenous catalytic reactions, so fundamental understanding of how water affects OC-O, C-OH, CO-H, C-H and C-C bond cleavages will give us valuable insight into how and why water influences selectivity of oxygenates decomposition, further enabling bottom up design of effective catalyst and catalyst system. Here we present a density functional theory (DFT) calculations of how water affects the elementary reaction steps involved in acetic acid decomposition over Pd and Pt (111) using micro-solvation, focusing on the critical elementary reaction steps that influence the selectivity between carbon monoxide (CO) and carbon dioxide (CO₂) formation. Our results suggest that water decreases the barrier for dehydrogenation of the OH group via H shuttling while it increases the barrier and endothermicity for the OC-O bond cleavage of (CH_XCOO; x = 0,1,2,3) to (CH_XCO; x = 0,1,2,3), which are important intermediates leading to CO formation. These calculations give insight into how water can affect the selectivity of acetic acid decomposition by influencing various elementary reaction steps differently, changing the selectivity of a complex decomposition mechanism.