Velocity components in the desorbing product CO2 in CO oxidation over Pd(100) under steady-state conditions

Abstract

The velocity distributions of desorbing product CO₂ were studied in the steady-state CO oxidation on Pd(100) by means of cross-correlation time-of-flight techniques. CO₂ desorption is sharply collimated along the surface-normal throughout the switching region of the rate-determining step. At O₂ pressures above 1×10⁻³ Torr and surface temperatures below ca. 520 K, the velocity distribution curve showed two components in the inhibited region where the overall reaction rate was controlled by O₂ dissociation. One component showed a translational temperature of 1500–2000 K and the other equaled the surface temperature. On the other hand, only the fast component was found in the velocity distribution curves in the active region where the reaction rate was controlled by CO adsorption, or in both regions below 1×10⁻³ Torr O₂ and above 520 K. The fast component showed a remarkable surface-structure dependence of the translational energy.