Co–Ru Nanoalloy Catalysts for the Acceptorless Dehydrogenation of Alcohols

Abstract

The synthesis of Co–Ru bimetallic nanoparticles was performed by co-reduction of Co­(II) and Ru­(III) salts in octan-1-ol, acting both as a solvent and a mild reducing agent. The metal composition was varied in the entire range, from pure Co to pure Ru. Although Co and Ru are miscible in the bulk, the formation of nanoalloys is not straightforward and requires careful selection of reaction parameters such as the nature of the solvent and that of the metal precursors. The formation of nanoalloys was unambiguously evidenced by HAADF STEM–EDX analyses. The particle size and the size dispersity were found to decrease with increasing Ru amount, yielding very small and monodisperse particles for the richest compositions in Ru. The unsupported particles were tested for the acceptorless alcohol dehydrogenation using (±)-octan-2-ol and octan-1-ol as model substrates. The results clearly show a synergetic effect since the bimetallic particles exhibit better performances than their monometallic counterparts.

Mechanism of formation of Co–Ru nanoalloys: the key role of Ru in the reduction pathway of Co

“…1b–d) and HAADF-STEM coupled to EDX analyses reveals the formation of alloys as reported in a previous study. 33 In contrast, large aggregates are isolated for pure Co and nanoflowers corresponding to the agglomeration of particles with a size of a few nanometers were obtained for pure Ru (see Fig. 1e and f).…”

“…This suggests that the particles are not totally homogeneous, in line with previously published results. 33 This will be further discussed when analyzing the EXAFS data at the Co K-edge.…”

“…The preparation of the Co x Ru 100− x samples has been reported elsewhere. 33 Briefly, Ru(acac) 3 and Co(acac) 2 are dissolved at room temperature (RT) in octan-1-ol with the targeted molar ratio and a global metallic concentration of 16.3 mmol L −1 and flushed with Ar. The solution was then heated up to the boiling point, ca.…”

“…11 Depending on the solvent and metal salt precursor, we obtained either bimetallic nanoparticles or a mixture of monometallic ones. 33 The formation of homogeneous structures necessitates either the simultaneous reduction of the two metal ions which nucleate and grow together to generate alloy nanocrystals, 11,36 the formation of a core shell structure followed by interdiffusion or a dissolution-reprecipitation process. Understanding the reaction pathway and the key parameters controlling the atomic arrangement (leading either to segregation or mixing) is of outmost importance to tailor NPs with tunable properties.…”

“…We also recently evidenced that Co x Ru 100− x alloy nanoplatelets show better catalytic activity towards the acceptor-less dehydrogenation of alcohols than their monometallic counterparts. 33 The synthetic method consisted in co-reducing acetylacetonate Co( ii ) and Ru( iii ) precursors in octan-1-ol at the boiling point. Co and Ru are theoretically miscible elements in the bulk state.…”