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 O-2 preadsorbed Pt(111) surface, (2) CO on the nearly perfect Pt(111) p(2x2)-O surface, and (3) CO on the disordered atomic oxygen-preadsorbed Pt(111) surface. Four CO2 desorption peaks (alpha-CO2 at 125 K, beta(3)-CO2 at similar to 225 K, beta(2)-CO2 at similar to 260 K, and beta(1)-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 alpha-CO2 state, beta(2,3)-CO2 states, and beta(1)-CO2 State are correlated with adsorbed O-2, disordered oxygen atoms, and p(2 X 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. (C) 1995 American Institute of Physics.