Thermal excitation of oxygen species as a trigger for the CO oxidation on Pt(111)

Thermal excitation of adsorbed oxygen species is found to initiate the CO oxidation on Pt(111). We have prepared three different coadsorption systems to study the reactivity of different oxygen species; (1) CO on the O2 preadsorbed Pt(111) surface, (2) CO on the nearly perfect Pt(111) p(2×2)-O surface, and (3) CO on the disordered atomic oxygen-preadsorbed Pt(111) surface. Four CO2 desorption peaks (α-CO2 at 125 K, β3-CO2 at ∼225 K, β2-CO2 at ∼260 K, and β1-CO2 at 320 K) are observed. The desorption temperatures of CO2 strongly depend on the adsorbed states of oxygen species. We have shown that the α-CO2 state, β2,3-CO2 states, and β1-CO2 state are correlated with adsorbed O2, disordered oxygen atoms, and p(2×2) oxygen atoms, respectively. The difference in CO2 desorption temperature is related to thermal excitation of each oxygen species, which is derived from the structural information of coadsorbed states during thermal evolution by means of low-energy electron diffraction and infrared reflection absorption spectroscopy.