Hydrogenation of nitrobenzene with supported platinum catalysts in supercritical carbon dioxide: effects of pressure, solvent, and metal particle size

Hydrogenation of nitrobenzene (NB) has been investigated with Pt/C catalysts in supercritical carbon dioxide (scCO2) and ethanol. The selectivity of aniline (AN) in scCO2 is ⩾80%, which is twice as high as that in ethanol, in which comparable amounts of AN and azobenzene (AB) are produced. In scCO2, the overall conversion of NB increases with CO2 pressure, has a maximum at around 10 MPa, and then decreases at 14 MPa. The product selectivity in scCO2 does not change much with the size of Pt particles while, in ethanol, the selectivity to AN and AB changes slightly with the particle size. The overall hydrogenation of NB is not structure sensitive in scCO2, while it is structure sensitive in ethanol in which turnover frequency tends to decrease with an increase in the degree of Pt dispersion.