CO 2 desorption dynamics on specified sites and surface phase transitions of Pt(110) in steady-state CO oxidation

Abstract

The spatial and velocity distributions of desorbing product CO2 were studied in the steady-state CO oxidation on Pt(110) by cross-correlation time-of-flight techniques. The surface structure transformation was monitored by LEED in the course of the catalyzed reaction. In the active region, where the surface was highly reconstructed into the missing-row form, CO2 desorption split into two directional lobes collimated along 25° from the surface normal in the plane including the [001] direction, indicating the CO2 formation on inclined (111) terraces. The translational temperature was maximized at the collimation angle, reaching about 1900 K. On the other hand, CO2 desorption sharply collimated along the surface normal at CO pressures where (1×2) domains disappeared. The distribution change from an inclined desorption to a normally directed one was abrupt at the CO pressure where the half-order LEED spot already disappeared. This switching point was more sensitive than LEED towards the complete transformation from (1×2) to (1×1) and was then used to construct a surface phase diagram for working reaction sites in the pressure range from 1×10−7 Torr to 1×10−4 Torr of oxygen. The turnover frequency of CO2 formation was enhanced on (1×2) domains with increasing CO pressure.