Hydrogenation of phenol in scCO2 over carbon nanofiber supported Rh catalyst

A catalyst of Rh nanoparticles supported on a carbon nanofiber, 5 wt.% Rh/CNF, with an average size of 2–3 nm has been prepared by a method of incipient wetness impregnation. The catalyst presented a high activity in the ring hydrogenation of phenol in a medium of supercritical CO2 (scCO2) at a low temperature of 323 K. The presence of compressed CO2 retards hydrogenation of cyclohexanone to cyclohexanol under the reaction conditions used, and this is beneficial for the formation of cyclohexanone, increasing the selectivity to cyclohexanone. But the selectivity to cyclohexanone is very low at the completion of reaction in the absence of CO2, at low CO2 pressures, and in the presence of pressurized N2 instead of CO2. That is, high selectivity to cyclohexanone can be achieved with CO2 species at higher pressures but not with the application of an inert hydrostatic pressure on the liquid substrate phase.