Chemical adsorption of acetic acid and deuterated acetic acid on Ru(0001), by RAIRS

The adsorption and thermal decomposition of acetic acid and deuterated acetic acid on clean Ru(0001) were studied by reflection absorption infrared spectroscopy. Acetic acid adsorbs molecularly, with dimer formation, at 100 K. At 113 K, the molecular form is still predominant, although some dissociative adsorption already occurs. Dehydrogenation is complete at 123 K, leaving adsorbed acetate as a symmetric bidentate species. Depending on coverage, two bonding configurations are proposed: a bidentate bridging [mu(2)-eta(2)(O,O)-CH3COO], with each oxygen bonded to a. neighbour Ru atom, at low coverages, and a bidentate chelating [eta(2)(O,O)-CH3COO], with the two oxygen atoms bonded to the same Ru, at higher coverages. The decomposition temperature increases with coverage, giving evidence in favour of a stabilizing effect of acetate ions and decomposition products on neighbour adsorbed acetates. For high enough coverages, adsorbed acetate was still detected at 500 K, proving the high stability of this surface species on Ru(0001). The adsorption of deuterated acetic acid gave consistent results, although dissociative adsorption starts occurring at 123 K and complete dehydrogenation occurs at 133 K, similar to 10 K above the respective temperatures for acetic acid. (C) 1998 Elsevier Science B.V. All rights reserved.