Acetic acid decomposition on Ni(100): Intermediate adsorbate structures by reflection infrared spectroscopy

Temperature-programmed reflection absorption infrared spectroscopy (TPRAIS), in concert with reflection absorption infrared spectroscopy (RAIS), was used to follow the sequence of stable surface intermediates for the decomposition of acetic acid monomer and dimer on Ni(100). After acetic acid monomer adsorbs molecularly at 170 K, the acid hydrogen is irreversibly lost at 240 K and a bridge-bonded acetate is formed. The bridge-bonded acetate then undergoes a reversible transformation to a monodentate acetate above 320 K which eventually decomposes to CO₂, C(ad), and H₂ at 435 K. Acetic acid dimer adsorbs molecularly at 170 K with the hydrogen-bonded ring approximately parallel to the surface. The dimer decomposes by dehydration at 255 K to adsorbed CO, a bridge-bonded acetate, and an adsorbed methyl group. The acetate decomposes to CO₂, C(ad), and H₂ at 440 K. The key step in the acetate decompositions is the C-C bond scission. The dynamic infrared study shows the importance of performing the spectroscopy at reaction conditions to identify the stable molecular configurations involved during the reaction.