Dynamics on Individual Reaction Sites in Steady-State Carbon Monoxide Oxidation on Stepped Platinum(113)

Abstract

The reaction kinetics and dynamics of carbon monoxide oxidation on a stepped Pt(113) = (s)2(111) × (001) surface were studied by angle-resolved kinetic and velocity measurements at the steady state. CO2 desorption sharply collimated nearly along either the (111) site normal or the (001) site normal. Only two reaction sites, the (111) and (001) sites, were operative. The translational energy of CO2 was characteristic of each site throughout a site switching. At surface temperatures above 520 K in the active region, where the reaction was first order in CO, the preference of the (111) site was suppressed with increasing CO pressure. Below 520 K, on the other hand, site switching slowly took place under limited conditions, in which both sites considerably contributed to the reaction and a meta-stable adsorbed phase seemed to be formed. The preference for the (111) site over the (001) site was caused by the former's higher reactivity of oxygen.

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

“…The sharpness of the angular distribution of each component was considered in the calculation. 6 The CO 2 formation proceeds mostly on the ͑1ϫ2͒ domains, and the contribution from the normally directed component is always minor, except for above the site-switching or far below the kinetic transition point. Figure 12͑d͒ shows the half-order spot intensity plotted against CO pressure.…”

“…The latter component was insignificant even at this azimuth. In the highly inhibited region, the distribution became broader and was approximated as cos 6 ͑Fig. 9͒.…”

“…32 This kind of energy comparison has only been reported on Pt͑113͒͑1ϫ2͒ϭ͓s͔3͑111͒ϫ3͑001͒, which consists of three-atom wide ͑111͒ and ͑001͒ facets oriented differently. 6 Under steady-state CO oxidation conditions at 3ϫ10…”

“…However, only a few reports have been published on the product desorption dynamics on individual formation sites. 6 One of the difficulties in this kind of work is the site identification itself. The angular distribution becomes useful to identify the formation sites when they are oriented in different directions.…”

Internal-energy measurements of angle-resolved product CO2 in catalytic CO oxidation by means of infrared chemiluminescence

“…4 In AR product desorption analysis, surface-structural information is directly provided from the reaction event as the polar and azimuthal angle dependences of the flux or both kinetic and internal energies. 4,[23][24][25][26] The internal energy would vary over these angles because the translational excitation is coupled with the rotational and vibrational ones in both adsorption and desorption processes. 13,14 The internal energy of desorbing products, however, has been analyzed in non-AR ways using infrared emission or absorption, resonance-enhanced multiphoton ionization ͑REMPI͒, 3,17 and electron beam or laser-induced fluorescence.…”