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 CO 2 were studied in the steady-state CO oxidation on Pt͑110͒ 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, CO 2 desorption split into two directional lobes collimated along 25°from the surface normal in the plane including the ͓001͔ direction, indicating the CO 2 formation on inclined ͑111͒ terraces. The translational temperature was maximized at the collimation angle, reaching about 1900 K. On the other hand, CO 2 desorption sharply collimated along the surface normal at CO pressures where ͑1ϫ2͒ 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 ͑1ϫ2͒ to ͑1ϫ1͒ and was then used to construct a surface phase diagram for working reaction sites in the pressure range from 1ϫ10 Ϫ7 Torr to 1ϫ10 Ϫ4 Torr of oxygen. The turnover frequency of CO 2 formation was enhanced on ͑1ϫ2͒ domains with increasing CO pressure.

A mechanistic study of CO removal on a small H-saturated platinum cluster

“…Thermochemically, the adsorbed CO 2 molecule can be readily desorbed from the cluster via an exothermic process of −0.45 eV with a small desorption barrier of 0.24 eV (Figure 1(b)). Our results indicate that the oxidation process at a high H-coverage is the rate-determining step and CO 2 desorption from the cluster is facile, which is consistent with the experimental observations [44][45][46] and theoretical predictions [42,27] for CO oxidation on crystalline surfaces.…”

Surface reaction dynamics and energy partitioning

“…This is reasonable because of the higher reactivity of oxygen on (111) terraces toward adsorbed CO. The oxygen on (001) facets can react with CO after most of the oxygen is consumed on (111) parts.The distribution of desorbing CO 2 varies when the surface structure changes [119]. For example, reconstructed Pt(110)(1×2) having three-atom wide terraces is converted into non-reconstructed (1×1) when the CO pressure exceeds a critical kinetic value at which the rate-determining step is switched from CO adsorption to oxygen dissociation.…”

Spatial distributions of desorbing products in basic catalytic processes and surface nano‐structures

“…3). 12 At the kinetic transition, the CO 2 formation decreases sharply, and the CO 2 desorption collimates along the surface normal when the CO pressure is high enough to reach about half a CO(a) monolayer to convert into the (1 × 1) form completely 27. This happens when the CO adsorption line yielding this coverage is below the kinetic transition line (see Fig.…”

“…The angular distribution changes sharply to the normally directed form when the CO pressure reaches the half‐monolayer CO adsorption line. Experimentally, this line was defined as the CO pressure at which both AR signals at θ = 25° and 0° become equal, and named the site‐switching point 12. Thus, the CO 2 desorption dynamics are separately examined in the above three regions, i.e., the active region (below the kinetic transition), the boundary region (between the kinetic transition and the site‐switching point), and the highly inhibited region (above the site‐switching point).…”