Comparison of bimetallic and trimetallic catalyst in reductive dechlorination; influence of copper addition

Efficiency of reduction of PCBs in aqueous solution was examined with the help of bimetallic catalyst Fe-C/Pd consisting of palladized grey cast iron and with a newly designed trimetallic catalyst (Cu-Fe-C/Pd) consisting of a copper metal plate with embodied microparticles of palladized grey iron (bimetallic catalyst). PCB solutions were prepared using DELOR 103. The trimetallic catalyst was significantly more efficient than bimetallic one. Trimetallic catalyst reduced concentration of PCBs to approximately 1% of its initial value during 70 minutes and bimetallic one during 48 hours. Moreover, more than 20% of declined PCBs were found adsorbed on the surfaces of the bimetallic catalysts. Contrary, presence of metal copper accelerates formation of the oxidation products and their release from the catalyst surface as the individual flocks which recovers activity of the trimetallic catalyst. These facts can significantly change the previous belief, widely published for decades that the reductive dechlorination of PCBs is the only decisive control step in the reduction of their content in water by zero valence metals. Keywords— PCB, reductive dechlorination, cast iron containing graphite, bimetallic and trimetallic catalysts, palladium, copper