Hydrogenation of anthracene in supercritical carbon dioxide solvent using Ni supported on Hβ-Zeolite catalyst

Catalytic hydrogenation of anthracene was studied over Ni supported on Hβ-zeolite catalyst under supercritical carbon dioxide (sc-CO₂) solvent. Hydrogenation of anthracene in sc-CO₂ yielded 100% conversion at 100 °C, which is attributed to the reduced mass transfer limitations, and increased solubility of H₂ and substrate in the reaction medium. The total pressure of 7 MPa was found to be optimum for high selectivity of octahydroanthracene (OHA). The conversion and selectivity for OHA increased with an increase in H₂ partial pressure, which is attributed to higher concentration of hydrogen atoms at higher H₂ pressures. The selectivity reduced the pressure below 7 MPa because of enhanced desorption of the tetrahydro-molecules and intermediates from Ni active sites, due to higher solubility of the surface species in sc-CO₂. The selectivity of OHA increased with the increase in catalyst weight and reaction time. The rate of hydrogenation of anthracene was compared with that found for napthalene and phenanthrene. The use of acetonitrile as co-solvent or expanded liquid with CO₂ decreased the catalytic activity.