| Abstract
| - The reactions of CO, NO, and NO with CO have been studied on Pt, Rh, and bimetallic Pt−Rh clustersdeposited on TiO2(110). The following four cluster surfaces were investigated: 4 ML of Rh, 4 ML of Pt, 2ML of Rh + 2 ML of Pt (Rh + Pt), and 2 ML of Pt + 2 ML of Rh (Pt + Rh). Scanning tunneling microscopystudies demonstrated that the surfaces exhibited similar cluster sizes and densities, and low-energy ion scatteringexperiments showed that the surfaces of the bimetallic clusters were Pt-rich (20−30% Rh) regardless of theorder of metal deposition; therefore, both Pt and Rh atoms are capable of diffusing to the cluster surface atroom temperature. Notably, heating the surface caused substantial encapsulation of the metal clusters bytitania at 700 K and complete encapsulation at 800 K. In temperature programmed desorption experiments,the activities of the Pt and Rh clusters for CO and NO dissociation were found to be higher than those of the(111) surfaces of the corresponding single crystals. For both reactions, the activities of the Rh + Pt and Pt+ Rh clusters were identical to each other and intermediate between that of pure Rh and pure Pt. For thereaction of NO with CO, the bimetallic clusters exhibited the greatest production of CO2 and the highestfraction of NO dissociation. On pure Rh clusters, CO2 production is inhibited by the preferential adsorptionof NO over CO, whereas on the pure Pt clusters, CO adsorption is favored over NO. Only the Pt−Rh surfacescan provide sites for both NO dissociation and CO adsorption that are necessary for facilitating CO2 formation.
|
