The Dynamics of the Steady-state CO Oxidation on Single Crystal Pd Surfaces. Identification of Reaction Site Using Infrared Chemiluminescence Technique.

Abstract

The internal energy distribution of C02 produced and desorbed in the steady-state CO oxidation (∼10-2 Torr) on well-defined single crystal Pd surfaces were successfully measured by using infrared (IR) chemiluminescence technique. The CO2 molecules produced on flat surface such as Pd(111) were highly excited (especially in terms of bending mode) than those on Pd(110) (1×1) which has atomically rough surface. These results show that the dynamics of CO oxidation on Pd surfaces is structure-sensitive. The difference in the vibrational distribution of the desorbing CO2 indicates that a structure of activated complex of CO2 is more bent on Pd(111) and relatively linear on Pd(110). Also, the kinetics of the steady-state CO oxidation is structure-sensitive. Furthermore, the IR chemiluminescence technique was applied to the study of CO2 on Pd(335) having both (111) terrace and step properties. The IR study on Pd(335) revealed that the steady-state CO oxidation is proceeding at step sites under higher surface temperature condition (850 K), and the active site of CO+O recombination reaction shifts to the terrace site with increasing CO coverage.