Enhanced N2 dissociation on Ru-loaded inorganic electride.

ABSTRACT

Electrides, i.e. salts in which electrons serve as anions, are promising materials for lowering activation energies of chemical reactions. Ab initio simulations are used to investigate the effect of the electron anions in a prototype mayenite-based electride (C12A7e(-)) on the mechanism of N2 dissociation. It is found that both atomic and molecular nitrogen species chemisorb on the electride surface and become negatively charged due to the electron transfer from the substrate. However, charging alone is not sufficient to promote dissociation of N2 molecules. In the presence of Ru, N2 adsorbs with the formation of a cis-Ru2N2 complex and the N-N bond weakens due to both the electron transfer from the substrate and interaction with Ru. This complex transforms into a more stable trans-Ru2N2 configuration, in which the N2 molecule is dissociated, with the calculated barrier of 116 kJ mol(-1) and the overall energy gain of 72 kJ mol(-1). In contrast, in the case of the stoichiometric mayentie, the cis-Ru2N2 is ~34 kJ mol(-1) more stable than the trans-Ru2N2, while the cis-trans transition has a barrier of 192 kJ mol(-1). Splitting of N2 is promoted by a combination of the strong electron donating power of C12A7e(-), ability of Ru to capture N2, polarization of Ru clusters, and electrostatic interaction of negatively charged N species with the surface cations.