Hydrogenation of Nitrobenzene with Supported Transition Metal Catalysts in Supercritical Carbon Dioxide

Abstract

Abstract Transition metal catalysts such as Pd, Pt, Ru, and Rh supported on carbon, silica and alumina have been examined for the hydrogenation of nitrobenzene (NB) in supercritical carbon dioxide (scCO 2 ) and in ethanol. The order of hydrogenation activity is Pt>Pd>Ru, Rh in scCO 2 and in ethanol. The effectiveness of the support is C>Al 2 O 3 , SiO 2 for either Pt or Pd in scCO 2 . For all the catalysts, higher selectivity to aniline has been obtained in scCO 2 compared with ethanol. Hydrogenation of nitrobenzene catalyzed with Pd/C and Pt/C catalysts was successfully conducted in scCO 2 with a 100% yield to aniline at a lower reaction temperature of 35 °C. The product aniline (organic phase) can be easily separated from the side‐product water (aqueous phase), solvent (scCO 2 ), and catalyst (solid) by a simple phase separation process. The hydrogenation of NB is a structure‐sensitive reaction in ethanol as well as in scCO 2 except for a few Pt/C catalysts in which the degree of metal dispersion is small (<0.08).