Enhancement of relatively non-toxic dechlorination of PCBs from thermal desorption off-gas over manganese-doped iron-based bimetallic catalyst

[Display omitted] •The in-situ degradation of PCBs in air conditions was explored.•Little off-gas was generated via the efficient, safe dechlorination technology.•The intermediate products (PCDFs) were completely reduced and dechlorinated.•Hydrodechlorination, preliminary oxidation, and deep oxidation were proposed.•The optimum content of Fe and temperature enhanced PCBs degradation. In view of the problems existing in catalytic degradation, such as low degradation efficiency, poor dechlorination efficiency and large amount of exhaust gas production, three iron-based bimetallic catalysts were developed for the dechlorination of polychlorinated biphenyls (PCBs) from thermal desorption off-gas, among which manganese-doped iron-based bimetallic catalyst showed the highest degradation efficiency (93.6%) and dechlorination efficiency (92.2%). Specifically, the effect of dechlorination under the air conditions was studied. The GC–MS analysis of intermediate products suggested the presence of three synergistic degradation pathways, namely, hydrodechlorination (HDC), preliminary oxidation, and deep oxidation over manganese-doped iron-based bimetallic catalyst. Through the hydrodechlorination, the chlorine atoms of PCBs were successively removed to obtain the final product biphenyl. During the oxidation stage including preliminary oxidation and deep oxidation, PCBs and intermediates were oxidized by reactive oxygen species (•OH and O2–•). This study provides an efficient and safe dechlorination technology of PCBs in the presence of oxygen with little exhaust gas generated.