Destabilization of adsorbed CO on the Pd(1 1 1) surface by subsurface carbon: Density functional studies

We employed periodic density functional slab model calculations and CO as probe molecule to examine the adsorption propensity of various sites of a Pd(1 1 1) substrate near subsurface carbon atoms. On all sites studied, CO adsorption is weakened compared to a clean Pd(1 1 1) surface. That destabilization, ∼50% at fcc sites directly above interstitial carbon and slowly decreasing at more distant hollow sites, is at variance with the conclusion recently derived from STM experiments, that subsurface impurities on Pd(1 1 1), tentatively assigned as interstitial atomic carbon species, are able to stabilize CO at nearby fcc adsorption sites.