Catalysts based on large size-controlled Pd nanoparticles for aqueous-phase hydrodechlorination

摘要

This work is aimed at evaluating the catalytic performance of Pd/C catalysts based on size-controlled nanoparticles (mean size 10-50 nm). Carbon black was used as support and the catalysts were tested in the aqueous phase hydrodechlorination of 4-chlorophenol. The Pd precursor was reduced with a methanol/water (10% vol.) mixture in the presence of PVP (PVP/Pd molar ratio 5-35) as capping agent. The performances of unsupported Pd-PVP colloidal nanoparticle and the catalysts prepared by impregnation of them on the carbon black (ex-situ synthesis), reduction of the precursor in the presence of that support (in-situ synthesis) and wetness impregnation were compared. The ex-situ preparation with less content of PVP (PVP/Pd molar ratio of 5) boosted the activity of the Pd-PVP nanoparticles from 16.8 to 167 mmol gPd - 1 min-1 showing the role of the support in enhancing the catalytic performance. The in-situ synthesis with less content of PVP (PVP/Pd molar ratio of 5) resulted in catalysts with lower activity than that prepared by ex-situ synthesis, although they exhibited higher ability to hydrogenate phenol to cyclohexanone and cyclohexanol, which can be related to the morphology of the nanoparticles synthesized. Regardless of the type of synthesis, as PVP dose in synthesis increased, activity and selectivity to hydrogenation products decreased. High activity values were obtained (20-167 mmol gPd - 1 min-1) taking into account the high mean size of the Pd nanoparticles in the catalysts