Preparation of [Ru6N] Clusters on MgO, K+/MgO, Cs+/MgO, and Al2O3 and the Reactivities with H2 and N2

Abstract

The supported ruthenium clusters [Rua] were prepared on MgO, K+/MgO, and Cs+/MgO from [Ru$\T(C0)161cluster as hydrogenation catalysts, stabilized, and chemically modified by nitrido nitrogen. The characterization and reactivities with H2 and N2 were investigated by EXAFS (extended X-ray absorption fine structure) in relation to their catalysis promoted by nitrido nitrogen. The [Ru~N] cluster unit was found to remain on MgO after heating in vacuum at 813 K (decarbonylated) and in H2 at 588 K (reaction condition of N2 hydrogenation), whereas the [RugN(C0)16]- cluster strongly interacted with the A1203 surface to degrade to [Ru~] by heating in vacuum at 813 K. The decarbonylated [Rua] framework also remained in H2 at 588 K on K+/MgO and Cs+/MgO without aggregation or degradation. By changing the Ru loading from 0.48 to 3.9 wt % on MgO, the coordination number NR~-o,, (O,,, oxygen atom at surface) decreased from 1.2 to 0.3, while the [Rua] cluster unit remained unchanged for samples with Ru loading up to -2.5 wt %. The preferable reaction of [R@] clusters with MgO(001) flat surfaces was suggested for the sample at 2.5 wt % Ru, but the cluster should have reacted mainly with lower coordination sites of MgO for the sample with lower Ru loading (-0.5 wt %). The rRu-o,, was shorter for [RU6N] on K+/MgO and Cs+/MgO (2.00-2.03 A) than on MgO (2.13 A), implying that the [Ru~N] was interacted with Os, atoms bonded to K+ or Cs+ ions to have a direct support effect of basic oxide K+/MgO or Cs+/MgO on catalysis. H-induced structure changes were observed for [RUsN]/MgO and [Ru$\T]-Cs+/MgO as the reversible changes on bonding distance rRu-Ru of 0.03 and 0.08 A, respectively, by the adsorptioddesorption of Hz. The adsorption of NZ was simple adsorption on [Ru~N] without structural change of [Ru~N] on MgO or Cs+/MgO.