The velocity and angular distributions of desorbing CO2 in CO oxidation on Pd(110) were studied under the steady-state conditions with cross-correlation time-of-flight techniques. Sharp changes were found in both distributions at the switching point of the rate-determining step. The velocity curves involved fast and slow components. The fast one, which was suddenly suppressed at the switching point, showed a translational temperature from 2300 to 4000 K. The slow component was thermalized to the surface temperature. A rapid site switching for CO2 formation is proposed, in which the fast component is formed on flat parts of the surface and the slow one is formed on structural defects.