Adsorption and thermal decomposition of benzene on the Pd(110)(1X2)-Cs surface: High-resolution electron energy loss spectroscopy, thermal desorption, and low-energy electron diffraction studies

The adsorbed state of benzene on the Pd(110)(1X2)-Cs surface at 90 K and its thermal decomposition process in the temperature region up to 650 K have been investigated by using high-resolution electron energy loss spectroscopy, multiplexed thermal desorption spectroscopy, and low-energy electron diffraction. Vibrational spectra show the existence of two chemisorbed states of benzene on Pd(110)(1X2)-Cs at 90 K. For a small exposure (≲0.3 langmuir, fractional coverage θ_C6H6 ≲ 0.07), benzene is predominantly adsorbed away from the Cs adatoms. With increasing exposure, the adsorbed benzene located near the Cs adatoms is formed additionally. The saturation coverage corresponds to 0.2 C₆H₆ molecule per Pd atom of the unreconstructed Pd(110) surface (θ_C6H6 = 0.2). For large exposure (>0.3 langmuir), a part of the adsorbed benzene is desorbed intact at about 300 and 330 K. The thermal decomposition of C₆H₆ occurs above 300 K, and the C_xH_y species (x = 1 or ≥3, y = 0, 1) and H atoms are formed on the surface. Only carbon adatoms remain on the Pd(110)(1X2)-Cs surface by heating to 650 K. These results are compared with those for the Pd(110) clean surface, and the effect of Cs adatoms on the surface reactions are discussed.