Zeolite-Confined Nano-RuO₂:  A Green, Selective, and Efficient Catalyst for Aerobic Alcohol Oxidation

Abstract

The development of green, selective, and efficient catalysts, which can aerobically oxidize a variety of alcohols to their corresponding aldehydes and ketones, is of both economic and environmental significance. We report here the synthesis of a novel aerobic oxidation catalyst, a zeolite-confined nanometer-sized RuO(2) (RuO(2)-FAU), by a one-step hydrothermal method. Using the spatial constraints of the rigid zeolitic framework, we sucessfully incorporated RuO(2) nanoparticles (1.3 +/- 0.2 nm) into the supercages of faujasite zeolite. Ru K-edge X-ray absorption fine structure results indicate that the RuO(2) nanoclusters anchored in the zeolite are structurally similar to highly hydrous RuO(2); that is, there is a two-dimensional structure of independent chains, in which RuO(6) octahedra are connected together by two shared oxygen atoms. In our preliminary catalytic studies, we find that the RuO(2) nanoclusters exhibit extraordinarily high activity and selectivity in the aerobic oxidation of alcohols under mild conditions, for example, air and ambient pressure. The physically trapped RuO(2) nanoclusters cannot diffuse out of the relatively narrow channels/pores of the zeolite during the catalytic process, making the catalyst both stable and reusable.

Water oxidation surface mechanisms replicated by a totally inorganic tetraruthenium–oxo molecular complex

“…It can be concluded that the Ru ions in the two materials have the same Ru(IV) oxidation state. These data compare well with those reported for related Ru(IV) systems (18). Instead, the main absorption edge of Ru(III)POM is shifted to lower photon energies (by 2 eV), which is consistent with a lower oxidation state of Ru.…”

“…The Ru(IV)POM and hydrous RuO 2 display identical XANES edge and line shape. The edge position is known to depend on the ruthenium oxidation state, shifting to higher photon energy as the valence state increases (17,18). It can be concluded that the Ru ions in the two materials have the same Ru(IV) oxidation state.…”

Catalytically active states of Ru(0001) catalyst in CO oxidation reaction

“…The results in this work apply well to real Ru catalyst systems, which are nano-particles forming amorphous oxide with not well-defined stoichiometry [34,35]. Such 'oxidized' states of the Ru nanoparticles, often described as Ru x O y , are comparable to the 'surface oxide' with subsurface oxygen rather than with the well-structured RuO 2 (110) surface.…”

Catalysis in flow: the practical and selective aerobic oxidation of alcohols to aldehydes and ketones

“…[11][12][13][14][15] In this work, Ru/Al 2 O 3 was chosen as it is commercially available at a reasonable cost, thus accessible to most synthetic laboratories.…”