Synergy Effect of Ru Single Atoms and Clusters on the MoS₂ Nanosheet for the Selective Hydrogenation of Nitroarenes

The MoS 2 nanosheets are acquired via a facile hydrothermal strategy, and the M/MoS 2 (M = Pt, Rh, Pd, Ru) samples are gained by impregnation. By comparing the catalytic behaviors of these catalysts for p -nitroacetophenone selective hydrogenation, it is found that the catalytic property and selectivity for one −NO 2 group hydrogenation of Ru/MoS 2 outperform those of other as-prepared catalysts. In addition, the Ru/MoS 2 catalysts with various Ru contents (0.37, 0.88, or 2.45 wt %) are used for 3-nitrostyrene selective hydrogenation, and the results show that 0.88 wt % Ru/MoS 2 displays the highest catalytic activity (turnover frequency) of TOF = 118.4 h –1 (TOF = 64.2 h –1 for 0.37 wt %Ru/MoS 2 and TOF = 61.7 h –1 for 2.45 wt %Ru/MoS 2 ) under the reaction conditions of 100 °C, 3.0 MPa H 2, and 1 h. The nanostructure characterization of the as-prepared catalysts (XRD, XPS, TEM, HRTEM, H 2 -TPD, XAS, AC-STEM, AC-STEM-EDX elemental mapping, and line scanning) demonstrate that Ru δ+ single atoms and Ru clusters are well dispersed on the support. Moreover, 0.88 wt % Ru/MoS 2 exhibits extremely high selectivity of one −NO 2 group hydrogenation (∼100%) at high conversion for other selected nitroaromatics’ hydrogenation, such as nitrobenzene, 2-chloronitrobenzene, 1,3-dinitrobenzene, 3-nitrostyrene, p -nitroacetophenone, and p -nitrobenzonitrile. This is mainly due to the fact that Ru is present with single atoms and clusters, producing the synergism of Ru δ+ single atoms, Ru clusters, and MoS 2 nanosheets. And the synergism mechanism is given below: hydrogen is preferentially adsorbed and activated at Ru clusters (forming activated H* species), the −NO 2 group is easily adsorbed and activated at Ru δ+ single atoms (charge interaction between electrons from O in −NO 2 and positive charge from Ru δ+ single atoms), and H* transfers to Ru δ+ single atoms by the hydrogen spillover effect of the MoS 2 nanosheets, reacting with the −NO 2 group, forming desired aromatic amines.