Improved Pd-on-Au bimetallic nanoparticle catalysts for aqueous-phase trichloroethene hydrodechlorination

摘要

Groundwater remediation through the catalytic breakdown of the undesired contaminants is a more effective and desirable approach than the conventional physical displacement methods of air-stripping and carbon adsorption.Palladium-on-gold nanoparticles(Pd/Au NPs)have recently been shown to catalyze the hydrodechlorination of trichloroethene in water,at room temperature,and in the presence of hydrogen,with the most active Pd/Au material found to be>70 times more active than Pd supported on alumina on a per-Pd atom basis.The potential of this catalyst as a groundwater remediation technology could be improved by synthesizing Pd/Au NPs with smaller diameters and immobilizing them on a solid support.For this study,we synthesized Pd/Au NPs with a core diameter of 4 nm and with different Pd loadings and studied them in colloidal form for aqueous-phase trichloroethene hydrodechlorination.The most active catalysts were considerably more active(>1900 L/g_(Pd)/min)than Pd NPs(55 L/g_(Pd)/min)and conventionally synthesized Pd/Al2O3(47 L/g_(Pd)/min).Accounting for a gas-liquid mass transfer effect and converting the Pd loading to Pd surface coverage using a magic cluster model for the Pd/Au NPs,the reaction rates in terms of initial turnover frequencies were>1.4,4.35 X 10~(-2),and 3.76 X 10~(-2)s~(-1),respectively.These materials exhibited volcano-like catalytic activity,in which hydrodechlorination rate was maximum near 70% Pd surface coverage.Au appeared to promote catalysis through geometric and electronic effects.Immobilization of the NPs on alumina,magnesia,and silica supports yielded active oxide-supported catalysts.