A green process for production of p-aminophenol from nitrobenzene hydrogenation in CO2/H2O: The promoting effects of CO2 and H2O

An efficient green process was developed for production of p -aminophenol (PAP) from hydrogenation of nitrobenzene (NB) over a traditional Pt/Al 2 O 3 catalyst in a reaction medium of supercritical CO 2 (scCO 2 ) and H 2 O without any additional acid catalyst involved. The combination of scCO 2 and H 2 O was confirmed to be effective for the production of PAP. The acidity, aroused by the in situ formed carbonic acid, increased with CO 2 pressure, which acted as acid catalysis during the reaction, and it can easily self-neutralize by depressurization of CO 2 , resulting in a green and a intensive process for it removed the final neutralization and salts disposal of the traditional liquid acids. Under the optimal reaction conditions, a high yield to PAP (68.9%) was achieved at the high conversion of NB (98.5%). Moreover, the results of in situ diffuse reflectance FTIR spectra revealed that CO was generated by the reverse water-gas shift reaction (CO 2   +   H 2   →   CO   +   H 2 O), it can adsorbed on the surface of Pt/Al 2 O 3 to suppress the undesired deep hydrogenation of N -phenylhydroxylamine (PHA) to aniline (AN), which also contributed to the obtained high selectivity of PAP. Therefore, the present green and efficient catalysis process will arouse the interest of researchers in the fields of the green and sustainable organic synthesis.