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 i nfrared spectroscopy. Acetic acid adsorbs molecularly, with dimer form ation, at 100 K. At 113 K, the molecular form is still predominant, al though 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 propose d: a bidentate bridging [mu(2)-eta(2)(O,O)-CH3COO], with each oxygen b onded to a. neighbour Ru atom, at low coverages, and a bidentate chela ting [eta(2)(O,O)-CH3COO], with the two oxygen atoms bonded to the sam e Ru, at higher coverages. The decomposition temperature increases wit h coverage, giving evidence in favour of a stabilizing effect of aceta te 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 ad sorption of deuterated acetic acid gave consistent results, although d issociative adsorption starts occurring at 123 K and complete dehydrog enation occurs at 133 K, similar to 10 K above the respective temperat ures for acetic acid. (C) 1998 Elsevier Science B.V. All rights reserv ed.