1208169-32-7Relevant articles and documents
Hydrogenation of phenol in supercritical carbon dioxide catalyzed by palladium supported on Al-MCM-41: A facile route for one-pot cyclohexanone formation
Chatterjee,Kawanami,Sato,Chatterjee,Yokoyama,Suzuki
, p. 1912 - 1924 (2009)
The hydrogenation of phenol has been carried out in supercritical carbon dioxide (scCO2) under very mild reaction conditions at the temperature of 50°C over palladium supported Al-MCM-41 (metal loading ～1%). This palladium catalyst is shown to be highly active and promotes the selective formation of cyclohexanone (～98%), an industrially important compound, in a "one-pot～ way. The effects of different variables like carbon dioxide and hydrogen pressure, reaction time and also silica/alumina ratio of the MCM-41 support along with palladium dispersion are presented and discussed. The pressure effect of carbon dioxide is significantly prominent in terms of conversion and cyclohexanone selectivity. Moreover, the silica/alumina ratio was also found to be an important parameter to enhance the effectiveness of the catalyst as it exhibits a remarkable increase in phenol conversion from 20.6% to 98.4% as the support changes from only silica MCM-41 to Al-MCM-41. A plausible mechanism for the hydrogenation of phenol to cyclohexanone over the palladium catalyst has been proposed. The proposition is vali-dated by transition state calculations using density functional theory (DFT), which reveal that cyclohexanone is a favorable product and stabilized by -1 over cyclohexanol in ScCO2 medium. Under similar reaction conditions, phenol hydrogenation was also carried out with rhodium, supported on Al-MCM-41. In contrast to the palladium catalyst, a mixture of cyclohexanone (57.8%) and cyclohexanol (42.2%) was formed. Detailed characterization by X-ray diffraction and transmission electron microscopy confirmed the presence of metal nanoparticles (palladium and rhodium) between 10-20 nm. Both the catalysts exhibit strikingly different product distributions in solventless conditions compared to scCO2. This method can also be successfully applied to the other hydroxylated aromatic compounds.
