Hydrogenation of phenol in aqueous phase with palladium on activated carbon catalysts

The hydrogenation of phenol in aqueous phase was studied in a continuous trickle bed reactor using commercial and some home-made Pd/activated carbon (AC) catalysts with the aim to explore a possible way for the treatment of phenolic wastewaters. The ranges studied for temperature, pressure and space-time (τ) were 110–170 °C, 2–9 bar and 0.5–3.1 kgcat h/mol, respectively. The inlet concentration of phenol was always 1000 mg/L. High conversion values for phenol were obtained at 150 °C and 9 bar in the case of the commercial catalyst. This catalyst has shown a convenient chemical stability in long-term experiments, being Pd leaching almost negligible. Different home-made catalysts were prepared and the influence of Pd load and precursor as well as the preparation conditions on the activity and selectivity have been investigated. The highest phenol conversion values were obtained with the catalysts calcined at 250 °C and reduced in hydrogen atmosphere at 150 °C, using palladium chloride as precursor. Moreover, these conditions led to a higher selectivity towards cyclohexanol, the less toxic product of the reaction pathway. The introduction of oxygen groups on the surface of the activated carbon through oxidation with nitric acid also improved the selectivity to cyclohexanol, thus leading to a higher reduction of the ecotoxicity.