Rapid transformation of 1,2,3,4-TCDD by Pd/Fe catalysts

Abstract

This study investigated reductive dechlorination of 1,2,3,4-tetrachlorodibenzo- p-dioxin (1,2,3,4-TCDD) in the presence of Pd/Fe, Cu/Fe and Ni/Fe bimetallic catalysts or zero-valent iron (ZVI) under aqueous and ambient temperature conditions. It was found that the Pd/Fe catalyst can rapidly transform 1,2,3,4-TCDD to chlorine-free dibenzo- p-dioxin (DD) with >95% of conversion and half lives on the order of 5 h, whereas Cu/Fe, Ni/Fe and ZVI were not reactive over 10 d. The dechlorination of 1,2,3,4-TCDD in the Pd/Fe systems was found to be stepwise, with 1,2,3-tri (TrCDD), 1,2-di (DCDD), and mono-(MCDD) chlorodibenzo- p-dioxins as the three intermediate products at low concentrations and DD as the final and dominant product. The reaction rate of 1,2,3,4-TCDD dechlorination appeared to decrease as the coverage of palladium on iron particle surface increases from 0.0060 mol% to 0.0228 mol%. Compared to our prior study of reductive dechlorination of 1,2,3,4-TCDD with zero valent zinc (ZVZ) as the reductant, the reactions with Pd/Fe bimetallic materials were relatively slower for TCDD, but much faster for TrCDDs and DCDDs, yielding DD as the major product. The study suggested that Pd/Fe bimetallic catalyst-based reactions may be suitable for rapid decontamination of polychlorinated dibenzo- p-dioxin/dibenzofuran (PCDD/F) polluted soils and sediments.