Structure sensitivity of NO adsorption on a smooth and stepped Pt(100) surface

Abstract

The adsorption of NO was studied in the temperature range 300–500 K by low-energy electron diffraction (LEED), photoemission, and Auger electron spectroscopy on a smooth Pt(100) crystal exhibiting a 1 × 1, 5 × 20, or √29 × √170 structure, and a stepped Pt [4(100) × (111)] crystal with 1 × 1 or reconstructed surface. The initial sticking coefficient of NO on all surfaces was about 0.6 at 300 K. Adsorbed molecular NO on the Pt(100)−l × 1 surface gave rise to a sharp c(2 × 4) type LEED pattern. A structure model for this pattern was proposed on the basis of nonlinearly bonded NO molecules. On heating the adsorbed NO molecules dissociated on all surfaces; the onset of dissociation was approximately at 400 K independent of structure and steps. No adsorption of NO could be observed on reconstructed surfaces at T > 380 K. On the other hand, unreconstructed surfaces were able to adsorb NO molecularly at temperatures up to 410 K and dissociatively at T = 423 and 435 K for the smooth and stepped surface, respectively. Dissociative NO adsorption was also verified for a carbon stabilized Pt(100)−1 × 1 surface at 473 K. We conclude that surface reconstruction can play a more significant role on NO adsorption kinetics than monatomic steps.