Highly effective catalysis of the double-icosahedral Ru19 cluster for dinitrogen dissociation – a first-principles investigation

Abstract

The N₂ bond cleavage is the rate-limiting step in the synthesis of ammonia, and ruthenium is a catalyst well known for this reaction. The double-icosahedral (D_5h) Ru₁₉ cluster is famous as an active catalyst, and has a remarkable stability towards the adsorption of H₂, N₂ and CO. Using first-principles calculations, we have investigated the adsorption and dissociation of dinitrogen on a double-icosahedral Ru₁₉ cluster. Our results show that the hollow site in the rhombus region (BHB site) of the Ru₁₉ cluster possesses the greatest catalytic activity to dissociate N₂, with the reaction barrier of 0.89 eV and an exothermicity of −1.45 eV. Multiple coadsorption of N₂ on the cluster (i.e. coadsorption of 2N₂ and 3N₂ on a single Ru₁₉ cluster) causes the barrier to dissociate N₂ to be less on a BHB site than for adsorption of a single N₂. To understand the catalytic properties of a Ru₁₉ cluster towards N₂ bond cleavage, we calculated the electron population, vibrational wavenumbers and local densities of states; the results are explicable.