Mechanisms of the CO oxidation on the Pd(110)c(2 × 4)-O surface

Abstract

The Pd(110)c(2 × 4)-O surface was exposed to various amounts of CO at 90 K, and the reaction-rate-limited CO 2 desorption was studied by thermal desorption spectroscopy (TDS). The results were correlated with those of high resolution electron energy loss spectroscopy (EELS) and low-energy electron diffraction (LEED). As the temperature is increased (heating rate 4 K s −1), the sizes of the c(2 × 4)-O patches become smaller with the remaining O atoms located in the quasi-three-coordinated sites until the CO 2 desorption is completed. The CO molecules are mobile beyond 200 K. The CO 2 desorption occurs as soon as the CO admolecules obtain sufficient translational kinetic energy to approach O adatoms (at the peripheries of the c(2 × 4)-O patches) in close proximity. Three CO 2 desorption peaks were observed which are directly correlated with three different adsorbed sites of CO. These results are quite different from the CO 2 desorptions on Pd(111) and Pd(100) surfaces. The CO 2 desorptions from CO on other oxygen-covered Pd(110) surfaces, i.e. (2 × 3)-1D, c(2 × 6), “complex” and pseudo-(2 × 1), were also briefly investigated. The CO 2 desorption peaks were observed which are correlated with unstable O and subsurface O. A CO 2 desorption peak was also observed which occurs by the direct interaction of O 2 molecules with CO on the c(2 × 4)-O surface.