Catalytic oxidation of gaseous PCDD/Fs with ozone over iron oxide catalysts Hou Chuan Wang a,b , Shu Hao Chang a , Pao Chang Hung a , Jyh Feng Hwang b , Moo Been Chang a, * a Graduate Institute of Environmental Engineering, National Central University, Chungli 320, Taiwan b Energy and Environment Research Laboratories, Industrial Technology Research Institute, Hsin-Chu 310, Taiwan Received 11 May 2007; received in revised form 17 August 2007; accepted 17 August 2007 Available online 24 October 2007 Abstract Catalytic oxidation of PCDD/Fs (polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans) with ozone (catalytic ozon- ation) over nano-sized iron oxides (denoted as Fe x O y ) was carried out at temperature of 120–180 °C. The effects of operating temper- ature, ozone concentration, space velocity (SV) and water vapor contents on PCDD/F removal and destruction efficiencies via catalytic ozonation were investigated. High activity of the iron oxide catalyst towards PCDD/F decomposition was observed even at low temperatures with the aid of ozone. The PCDD/F removal and destruction efficiencies achieved with Fe x O y /O 3 at 180 °C reach 94% and 91%, respectively. In the absence of ozone, the destruction efficiencies of all PCDD/F congeners are below 20% and decrease with increasing chlorination level of PCDD/F congener at lower temperature (120 °C). However, in the presence of ozone, the destruc- tion efficiencies of all PCDD/F congeners are over 80% on Fe x O y /O 3 at 180 °C. Higher temperature and ozone addition increase the activity of iron oxide for the decomposition of PCDD/Fs. Additionally, in the presence of 5% water vapor, the destruction efficiency of the PCDD/Fs is above 90% even at lower operating temperature (150 °C). It indicates that the presence of appropriate amount of water vapor enhances the catalytic activity for the decomposition of gas-phase PCDD/Fs. Ó 2007 Elsevier Ltd. All rights reserved. Keywords: Catalytic ozonation; Dioxins; Iron oxide; Ozone; Space velocity 1. Introduction Activated carbon injection (ACI) technology is com- monly used to reduce PCDD/F (polychlorinated dibenzo- p-dioxins and polychlorinated dibenzofurans) emissions from stationary sources including municipal waste inciner- ators (MWIs). However, ACI technology only transfers gaseous PCDD/Fs to the solid phase (fly ash) and further treatment is needed for the disposal of fly ash which con- tains relatively high level of PCDD/Fs. Additionally, ACI may increase the total PCDD/F discharge from muni- cipal waste incinerators because it brings extra carbon source to the system (Chang and Lin, 2001). Relevant studies indicate that catalytic process can sup- press dioxin formation. Ferric oxide has been tested as a catalyst to oxidize CO and suppress PCDD/F formation in the furnace (Imai et al., 2001; Hung and Lin, 2003). Besides, some catalysts operated at appropriate tempera- tures also cause complete destruction of PCDD/Fs, result- ing in the formation of CO 2 ,H 2 O and HCl (Ide et al., 1996; Liljelind et al., 2001). Noble metals (Pt, Pd and Au) (Becker and Forster, 1997; Scire et al., 2003) and transition metal oxides (CrO x , MnO x , VO x , WO x and MoO x )(Krish- namoorthy et al., 2000; Liu et al., 2001; Yim et al., 2002; Cho and Ihm, 2002) catalysts are two major classes used for catalytic oxidation of dioxins or dioxin-like 0045-6535/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.chemosphere.2007.08.041 * Corresponding author. Tel./fax: +886 3 4226774. E-mail address: mbchang@ncuen.ncu.edu.tw (M.B. Chang). www.elsevier.com/locate/chemosphere Available online at www.sciencedirect.com Chemosphere 71 (2008) 388–397