Activity enhancement and selectivity tuneability in aqueous phase hydrodechlorination by use of controlled growth Pd-Rh nanoparticles

Abstract

Colloidal bimetallic PdRh nanoparticles (NPs) of controlled size and structure were synthesized and tested as catalysts models in aqueous phase hydrodechlorination (HDC) (303K, 1atm) using 4-chlorophenol (4-CP) as target compound. The colloidal bimetallic PdRh NPs were synthesized by chemical reduction, using methanol as reducing agent and poly(N-vinyl-2-pyrrolidone) (PVP) as capping agent. Two methods of synthesis (co-reduction, successive reduction) and three different Pd/Rh nominal molar ratios (0.2, 1, and 5) were used. The NPs were characterized by means of TEM, HAADF-STEM/EDS and XPS.High 4-CP conversion values (85–100%) were achieved at very low metal concentration (1.23×10−3gL−1). Phenol, cyclohexanone, cyclohexanol, and cyclohexene were the reaction by-products detected. Core–shell and cluster-in-cluster NPs structures were obtained by varying the method of synthesis and the Pd/Rh molar ratio. The activity was found to increase with the Pd/Rh ratio. Activity values up to 67.0mmolg−1min−1, which are significantly higher than those obtained in previous works with monometallic Pd (39.1mmolg−1min−1) and Rh (29.4mmolg−1min−1) under equivalent conditions, were achieved. Significant differences in activity and selectivity were found between the NPs with Pd/Rh ratios of 0.2–1 synthesized by co-reduction and successive reduction. The results indicate that the study of the performance of Pd/Rh bimetallic catalysts in HDC requires some consideration about the structure of the NPs, since the metal arrangement can determine an enhancement in the activity of the catalysts.