Low temperature degradation of polychlorinated dibenzo-p-dioxins and dibenzofurans over a VO_x-CeO_x/TiO_2 catalyst with addition of ozone

摘要

In order to find a catalyst to destroy polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) with high efficiency, a homemade VOx-CeOx/TiO2 catalyst was prepared, and then tested in the flue gas of a waste incinerator at temperatures of 180-240 degrees C. The results shows the best removal efficiency (93.4%) was attained already at 200 degrees C, yet degradation efficiency further raised with temperature, until 240 degrees C. Ozone (500 ppm) was also introduced into the system to increase the activity of catalyst, and removal efficiency of PCDD/Fs increased further to 97.4% and 98.8% at 200 and 240 degrees C, respectively. In addition, a lab-scale reaction system was installed to study the degradation mechanism of PCDD/Fs. Octa-chlorinated dibenzo-p-dioxin (OCDD) was selected as the study object due to the most stable structure and maximum chlorine atom number. The intermediate products resulting from the conversion of OCDD were monitored using gas chromatography/mass spectrometry and Fourier transform infrared spectroscopy and a possible reaction pathway was proposed. Dechlorination persists until the complete conversion of OCDD. Oxidation decomposes OCDD-molecules mainly into organic substances having one, two or more benzene rings, yet also alkanes, cycloalkanes and heterocompounds of sulphur, nitrogen, and halogens appear. However, more work is still needed to fit those trace products into mechanistic schemes. (C) 2018 Elsevier Ltd. All rights reserved.