CO adsorption and oxidation on Pd(110)-c(2x4)-O by reflection-absorption infrared spectroscopy

Adsorption and oxidation of CO on Pd(110)-c(2 x 4)-O were investigated by reflection-absorption infrared spectroscopy (RAIRS), low-energy electron diffraction (LEED), and temperature-programmed reaction (TPR). High-frequency CO at 2140 cm(-1), which was greatly influenced by adsorbed oxygen atoms, was observed by RAIRS even at low CO coverage when the Pd(110)-c(2 x 4)-O surface was exposed to CO at 100 K. This peak developed along with a broad band around 2000 cm(-1) from low CO coverage to the saturation. The reaction of CO and an oxygen atom to form COP on the c(2 x 4)-O surface was observed in the range 100-450 K. Below 250 K, two desorption peaks of CO2 were observed in TPR spectra and the corresponding RAIR spectra showed that Linear CO species (2140-2070 cm(-1)) disappeared by desorption as CO dr reaction with an oxygen atom to form CO2, while there was little decrease of bridge CO species (2020-1880 cm(-1)), It is likely that Linear CO species mainly reacted to form CO2 on Pd(110)-c(2 x 4)-O below 250 K. We successfully followed the constant-flow reaction of CO and O-2 On the Pd(11O)-c(2 x 4)-O at 220 K; however, the reaction ceased with an increase of bridge CO at 1992 cm(-1). RAIR spectra during the reaction of CO and O above 250 K suggest that CO began to form domains separated from oxygen atoms and the substrate structure of (1 x 2) was gradually converted into (1 x 1) according to the local coverage of CO.