Competitive CN and N2 formation on Rh(111) : a case of entropic stabilization

Cyanide formation and nitrogen recombination on Rh(1 1 1) have been studied using density functional theory. CN can interact with the surface via several adsorption modes, all of them within a very narrow range of adsorption energies. CN can be regarded as a highly mobile species on the surface, and dissociation is associated with a considerable loss of entropy, which is by no means compensated from an energetic point of view. Consequently, CN dissociation is largely unfavored, which agrees with the experimentally observation that CN is stable for a wide range of temperatures on Rh(1 1 1) (450-850 K)