Carboxylic acid adsorption on NiO(100) characterized by X-ray photoelectron and high resolution electron energy loss spectroscopies

Formic, acetic and propionic acids have been adsorbed onto NiO(100) at 300 K and the resulting species characterized by X-ray photoelectron spectroscopy (XPS) and high resolution electron energy loss spectroscopy (HREELS). As do many ionic solids, nickel oxide possesses a strong series of Fuchs-Kliewer multiple phonon losses, which obscures the weaker adsorbate vibrational structure. A novel phonon deconvolution procedure that removes multiple phonons has, therefore, been used in analyzing the HREELS data. NiO(100) exhibits amphoteric chemisorptive properties, dissociatively adsorbing the acids as carboxylates and surface hydroxyls. Adsorption saturates after approximately 10000 langmuir to yield one carboxylate for every two nickel sites. By stoichiometry, one half of all surface oxygen sites are assumed to be hydroxylated. A tilted carboxylate geometry is evident in the high value of thev_s(COO) vibrational mode observed in the HREEL spectra.