Influence of transition metal catalysts on the decomposition product distribution of PCBs and PCDD/Fs

Abstract

In this study, reliable and stable polychlorinated biphenyls (PCBs) and polychlorinated dibenzo-p-dioxins/dibenzofurans (PCDD/Fs) generation systems were used to investigate catalyst performance. The distribution characteristics of PCBs and PCDD/Fs after reaction were evaluated under different simulated flue gas conditions using NiO- and MnO2-loaded γ-Al2O3 and ZSM-5 catalysts. The results showed that the active metal of the catalyst affected mainly the decomposition efficiency, the substrate type affected the distribution characteristics of PCBs, and both the active metal and substrate type jointly determined the fingerprint distribution characteristics of PCBs. Moreover, there was an apparent marginal effect of the active metal loading on the same catalyst and the decomposition efficiency of the pollutants. In the temperature range of 100–350 °C, temperature variation had little effect on the removal efficiency of PCBs, but the gas–solid phase distribution characteristics of the pollutants changed significantly, and large amounts of di- and tri-CBs were generated in the products at 200 °C. A small amount of water generated hydrogen via the water–gas shift reaction at medium temperature, which promoted the hydro-dechlorination reaction of the chlorinated organics. However, excess water in the substrate gas competes with the pollutants for adsorption sites and reduces the reaction activity of the catalyst.