Dissociation of N2O promoted by Rh6 clusters. A ZORA/DFT/PBE study

• Reduction of the nitrous oxide (N2O) toxic molecule by neutral Rh6 clusters.
• Density functional theory calculations including ZORA relativistic effects.
• Dissociation of N2O by Rh6 as catalyst, without support or dopping substances.
• Active sites of the Rh6 + N2O reaction pathways, in different multiplicities.
• Rh6 is one of the smallest particles with many active sites, able to reduce N2O.

The interaction of Rh6 clusters with the nitrous oxide (N2O) molecule was studied by means of density functional theory (DFT) calculations through the zero-order-regular approximation (ZORA), which includes relativistic effects explicitly. The purpose of this work is to characterize the N2O reduction to N2 and O by Rh6 clusters. The identified low-lying and degenerate states of Rh6, octahedron with multiplicities of 1 and 7, and a triangular prism with a septet, present many active sites of reduction. The initial steps of the N2O + Rh6 reaction were studied through different adsorption modes, each one having different multiplicities. The RhRh bonds define the active sites to produce N2O dissociation. The most successful reaction pathway originates when the linear NNO molecule is approached parallel to the RhRh bonds, being this active site the most numerous in the systems. The NO bond breaks in five addressed multiplicities, with 2 and 3 degenerate energy cases in the octahedron. Other approaches studied are: N2O pointing toward the triangular or square face bisectors or to the surface between two RhRh bonds. In these two cases, the N2O molecule moves toward one of the RhRh bonds dissociating over it. Overall, to reduce N2O, the prism structure presents a greater number of different active sites, but the octahedron has more edges, in which the oxide can break. For each calculation, many parameters were obtained and are included in the text: vibrational frequencies, distances between atoms, binding energies, total electronic charges, as well as optimized geometries. An important result of this work is the feature that Rh6 is the smallest nanoparticle having several structures at the ground state, which greatly increases the number of active sites being able to reduce the nitrous oxide contaminant.

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