Low temperature decomposition of PCB by TiO2-based V2O5/WO3 catalyst: evaluation of the relevance of PCDF formation and insights into the first step of oxidative destruction of chlorinated aromatics

The reduction of polychlorinated biphenyls (PCB) emissions to the environme nt are contemporary issues of global efforts. Within this goal, the destruc tion of PCB is a challenge also for applied catalysis, in particular with r espect to the destruction of PCB waste and the off-gas cleaning of incinera tion facilities. In this study, PCB were destroyed on a V2O5/WO3 supported titanium catalyst at low temperature in the range of 150-300 degreesC. At a space velocity o f 5000 h(-1) more than 98% could be removed, Below 250 degreesC, the higher chlorinated PCB remained partly unchanged on the catalyst for several minu tes. In contrast, the oxidation process lasted up to hours at a temperature of 150 degreesC. At around 200 degreesC and below a significant part of the PCB were oxidise d to the more toxic polychlorinated dibenzofurans (PCDF). The PCDF remained mainly adsorbed on the catalyst. At 250 degreesC, no significant amount of PCDF were detected and at 300 degreesC no byproducts were found. The oxidation of selected individual PCB isomers and the isomer specific an alysis of PCDF formed give an insight into the initial step of degradation of chlorinated aromatics on V2O5/WO3-TiO2 catalysts. The results indicated that hydrogen abstraction is the preferred step and an initial abstraction of chlorine is only a minor pathway. This suggests an electrophilic oxygen transfer during the destruction of PCB. During the destruction experiments, a slight chlorination of the non-degrad ed PCB occurred. On the other hand, no measurable dechlorination/hydrogenat ion was observed. (C) 2001 Elsevier Science B.V. All rights reserved.