Quantification of lateral repulsion between coadsorbed CO and N on Rh(100) using temperature-programmed desorption, low-energy electron diffraction, and Monte Carlo simulations

Abstract

Temperature programmed desorption of CO coadsorbed with atomic N on Rh(100), reveals both long- and short-range interactions between adsorbed CO and N. For CO desorption from Rh(100) at low coverage we find an activation energy Ea of 137±2 kJ/mol and a preexponential factor of 1013.8±0.2 s−1. Coadsorption with N partially blocks CO adsorption and destabilizes CO by lowering Ea for CO desorption. Destabilization at low N coverage is explained by long-range electronic modification of the Rh(100) surface. At high N and CO coverage, we find evidence for a short-range repulsive lateral interaction between COads and Nads in neighboring positions. We derive a pairwise repulsive interaction ωCO–NNN=19 kJ/mol for CO coadsorbed to a c(2×2) arrangement of N atoms. This has important implications for the lateral distribution of coadsorbed CO and N at different adsorbate coverages. Regarding the different lateral interactions and mobility of adsorbates, we propose a structural model which satisfactorily explains the observed effects of atomic N on the desorption of CO. Dynamic Monte Carlo simulations were used to verify the experimentally obtained value for the CO–N interaction, by using the kinetic parameters and interaction energy derived from the temperature-programmed desorption experiments.