title: On the origin of high activity of hcp metals for ammonia synthesis.
abstract: Structure and activity of nanoparticles of hexagonal close-packed (hcp) metals are studied using first-principles calculations. Results show that, in contact with a nitrogen environment, high-index {134[combining macron]2} facets are formed on hcp metal nanoparticles. Nitrogen molecules dissociate easily at kink sites on these high-index facets (activation barriers of <0.2 eV). Analysis of the site blocking effect and adsorption energies on {134[combining macron]2} facets explains the order of activity of hcp metals for ammonia synthesis: Re < Os < Ru. Our results indicate that the high activity of hcp metals for ammonia synthesis is due to the N-induced formation of {134[combining macron]2} facets with high activity for the dissociation of nitrogen molecules. However, quite different behavior for adsorption of dissociated N atoms leads to distinctive activity of hcp metals.
authors.affiliation: Physical and Theoretical Chemistry, Freie Universität Berlin, Takustr. 3, 14195 Berlin, Germany. payam.kaghazchi@fu-berlin.de.
authors.forename: Shideh
authors.initials: S
authors.lastname: Ahmadi
authors.affiliation: Physical and Theoretical Chemistry, Freie Universität Berlin, Takustr. 3, 14195 Berlin, Germany. payam.kaghazchi@fu-berlin.de.
authors.forename: Payam
authors.initials: P
authors.lastname: Kaghazchi