Sputtering-deposition of Ru nanoparticles onto Al2O3 modified with imidazolium ionic liquids: synthesis, characterisation and catalysis

Abstract

Well-distributed Ru nanoparticles (Ru-NPs) were produced over Al₂O₃ supports modified with covalently anchored imidazolium ionic liquids (ILs) containing different anions and cation lateral alkyl chain lengths by simple sputtering from a Ru foil. These Ru-NPs were active catalysts for the hydrogenation of benzene. Furthermore, depending on the nature of the IL used to modify the support (hydrophilic or hydrophobic), different catalytic behaviours were observed. Turnover numbers (TON) as high as 27 000 with a turnover frequency (TOF) of 2.73 s⁻¹ were achieved with Ru-NPs of 6.4 nm supported in Al₂O₃ modified with an IL containing the N(SO₂CF₃)₂⁻ anion, whereas higher initial cyclohexene selectivities (ca. 20% at 1% benzene conversion) were attained for Ru-NPs of 6.6 nm in the case where Cl⁻ and BF₄⁻ anions were used. Such observations strongly suggest that thin layers of ILs surround the NP surface, modifying the reactivity of these catalytic systems. These findings open a new window of opportunity in the development of size-controlled Ru-NPs with tuneable reactivity.