Bimetallic Mn$_x$Ru$_{100–x}$ Nanoparticles on Supported Ionic Liquid Phases (Mn$_x$Ru$_{100–x}$ @SILP) as Tunable Hydrogenation Catalysts

Bimetallic manganese–ruthenium nanoparticles of defined Mn:Ru ratios were prepared on an imidazolium-based supported ionic liquid phase. Characterization of the resulting Mn$_x$Ru$_{100–x}$@SILP materials by electron microscopy evidenced the formation of small (1.3–3.6 nm) and well-dispersed nanoparticles (NPs) containing Mn and Ru in the expected ratios. X-ray absorption spectroscopy (XAS) studies revealed that no significant levels of alloying occurred in these NPs that contain mainly oxidized Mn species and metallic Ru, consistent with the immiscibility of the two metals and the high oxophilicity of Mn. The hydrogenation performance of Mn$_x$Ru$_{100–x}$@SILP materials was probed using benzylideneacetone as model substrate containing three distinct reducible moieties. Albeit the two metals are present in distinct phases, the Mn:Ru ratio was found to have a strong impact on activity and selectivity with trends similar to what was previously reported for alloyed Fe$_x$Ru$_{100–x}$@SILP and Co$_x$Ru$_{100–x}$@SILP catalysts. In particular, a sharp switch of 6-membered aromatic ring hydrogenation between Mn$_{15}$Ru$_{85}$ (full ring hydrogenation) and Mn$_{25}$Ru$_{75}$ (no ring hydrogenation) was observed. These results demonstrate that alloying is not a requirement to observe synergistic effects from the combination of 3d metals and noble metals in NPs, opening new opportunities for the development of bimetallic catalysts for selective hydrogenation.