Kinetic studies on the CO oxidation on Pd(111) with low energy electron diffraction (LEED) and angle-resolved thermal desorption

Abstract

Three different coadsorption structures of CO and oxygen over Pd(111) were analyzed through measurements of the intensity of LEED spots; separate domains of p(2×2)–O and ((3)1/2×(3)1/2)R30°–CO, closely contacted domains of ((3)1/2×(3)1/2)R30°–O with the same structure of CO, and also a mixed phase with (2×1) periodicity. The desorption of CO2 produced in the above adlayers was analyzed in an angle-resolved form. The angular distribution becomes extremely sharp, when the reaction sites are closely surrounded by coadsorbates. The collimation of the desorption along the surface normal is suggested to be due to the collision of desorbing CO2 with the surrounding adsorbates, as well as the repulsive interaction between nascent CO2 and the surface.