Unexpectedly high catalytic activity of Ruthenium catalysts in the hydrogenation of nitrobenzene

The performance of ruthenium nanoparticles as quasi-homogeneous catalyst for the concurrent hydrogenation of the nitro group and the aromatic ring in nitrobenzene was compared to a classic carbon supported Ru/C catalyst. When the tartaric acid and glycine based ionic liquids [TA2-][N+8888]2 and [Gly-][N+8888], respectively, were used for stabilizing the ruthenium nanoparticles, catalytic activity and selectivity to cyclohexylamine were similar to the Ru/C catalyst. In contrast, Ru nanoparticles stabilised with the dimethylglycine based ionic liquid [Me2Gly-][N+8888] provided high selectivity to aniline. With Ru/C, the hydrogenation of nitrobenzene was faster than of aniline. These observations were rationalised in terms of binding strength of the stabiliser and intermediates to the ruthenium surface and consequent changes in the elementary steps.