Highly dispersed rhodium atoms supported on defect-rich Co(OH) for the chemoselective hydrogenation of nitroarenes

Catalysts of 0.54% (Pt, Rh, Pd or Ru)/Co(OH) 2 and 1.23% Rh/Co(OH) 2 were successfully synthesized via simple hydrothermal and precipitation methods for the selective hydrogenation of nitroarenes. It was found that 0.54% Rh/Co(OH) 2 outperformed other catalysts, for example, 2-chloronitrobenzene hydrogenation (with a turnover frequency (TOF) of 575 h −1 ) under 3.0 MPa H 2 at 100 °C for 1 h (much higher than that of 1.23% Rh/Co(OH) 2 ; TOF, 398 h −1 ). Through characterization of the nanostructure (XRD, TEM, HRTEM, AC-STEM (spherical aberration-corrected scanning transmission electron microscopy), AC-STEM-EDX elemental mapping and line-scanning, H 2 -TPD, etc. ), it was confirmed that Rh was dispersed in the form of single atoms and ultrasmall nanoclusters on Co(OH) 2 for 0.54% Rh/Co(OH) 2 . Moreover, 0.54% Rh/Co(OH) 2 also exhibited high selectivity for -NO 2 hydrogenation for other selected nitroarene substrates hydrogenation reactions. This was mainly attributed to the presence of Rh as single atoms or super tiny nanoclusters in 0.54% Rh/Co(OH) 2 , leading to a significant increase in the number of active sites, beneficial adsorption of the -NO 2 -group at defect-rich Co(OH) 2 , and an interfacial synergy effect of Rh-Co(OH) 2 , thus improving the catalytic performance. 0.54% Rh/Co(OH) 2 exhibited 100% selectivity for -NO 2 hydrogenation at >96% conversion for nitroarene hydrogenation. Its excellent catalytic performance is due to the interfacial effect of Rh-Co(OH) 2 and Rh in the form of single atoms and nanoclusters.