Effects of co-adsorbed water on different bond cleavages involved in acetic acid decomposition on Pt (111)

Acetic acid decomposition on Pt (111) in the presence of co-adsorbed water is a good model system for oxygenate decomposition on Pt (111) in aqueous phase, with application in hydrogen production and biomass conversion. Here we present a density functional theory (DFT) theory calculation of how co-adsorbed water affects different bond cleavages of acetic acid decomposition on Pt (111). The presence of co-adsorbed water generally enhances OH bond cleavage while inhibiting OCO and OCOH bond cleavage. The influence of co-adsorbed water on CH bond cleavage varies the most and depends on the nature of the transition state and how co-adsorbed water stabilizes the initial and final state. Although these trends are useful as general guidance, they are not sufficient to predict the effect on a complex reaction network such as acetic acid decomposition on Pt (111) which has several parallel reaction paths with similar energies.

In the absence of co-adsorbed water, the two lowest energy pathways are decarboxylation (DCX) and decarbonylation (DCN) pathways through a common CH₂COO intermediate, in which the DCX pathway (CH bond cleavage of CH₂COO) is more favorable than DCN pathway (OCO bond cleavage of CH₂COO). In the presence of co-adsorbed water, the energy difference between CH bond cleavage and OCO bond cleavage of CH₂COO increases, suggesting an increase in the favorability of acetic acid decarboxylation (formation of carbon dioxide) over acetic acid decarbonylation (formation of carbon monoxide) on Pt (111).