Molecular Level Studies of Acetic Acid Adsorption and Reactions on Platinum and Nickel

Pt and Ni-based catalysts are actively studied in the development of imporoved technologies for the conversion of biomass-derived feedstocks into fuels and chemical feedstocks, specifically for hydrodeoxygenation and steam reforming of bio-oils. Since acetic acid is a component of bio-oils as well as a widely used model compound, it is important to better understand its reactivity on Pt and Ni catalytic surfaces at the molecular level. In this study, acetic acid adsorption and reactions on Pt(111) were studied with infrared reflection absorption spectroscopy (IRAS), temperature-programmed desorption (TPD) and density functional theory (DFT) calculations. The results were compared to Ni(111) and Ni(110) surfaces.<br/>At the dosing temperature of 90 K, acetic acid forms a physisorbed layer on Pt(111). At 140 K, acetic acid predominantly chemisorbs molecularly through its carbonyl oxygen atom. In addition, some dissociative adsorption is observed with the formation of acetate and hydrogen. Annealing to 193 K leads to a mostly complete conversion of molecularly adsorbed acetic acid to acetate species. At 440 K, acetate species decompose, evidenced by desorption of H₂, CO and CO₂. In contrast, due to differences in the adsorbed structures, acetate species decompose on Ni(110) at a lower temperature of 425 K. Above 425 K, only residual carbon remains on the Ni surface.