Direct Selective Hydrogenation of Phenol and Derivatives over Polyaniline-Functionalized Carbon-Nanotube-Supported Palladium

Abstract

Cyclohexanone is an industrially important intermediate in the synthesis of materials such as nylon and polyamides, but direct selective hydrogenation of phenol to cyclohexanone under green conditions is a challenge owing to the over-reduction of cyclohexanone to cyclohexanol. A catalyst made of palladium nanoparticles supported on polyaniline-functionalized carbon nanotubes, Pd–PANI/CNT, which was shown to be highly active towards the direct hydrogenation of phenol to cyclohexanone, is reported. Phenol conversion exceeding 99 % was achieved with a cyclohexanone selectivity of >99 % under atmospheric pressure of hydrogen in aqueous media. The generality of the catalyst for this reaction was demonstrated by selective hydrogenation of other hydroxylated aromatic compounds with similar performance, again under green and mild conditions. It is suggested the Pd–N interactions and polymeric stabilization play a key role in the formation of stable and highly dispersed palladium nanoparticles on the conducting composite material PANI/CNT. The results also indicate that the phenol conversion is related presumably to the conductive property of PANI/CNT, whereas the cyclohexanone selectivity is attributed to the nitrogen-containing nature of PANI/CNT.