Metal-loaded ZSM5 zeolites for catalytic purification of dioxin/furans and NOx containing exhaust gases from MWI plants: Effect of different metal cations

Abstract

A series of metal loaded ZSM5 including Cu/, Fe/, Mn/ and V/ was prepared and their catalytic activity, selectivity and durability were compared with the commercially used VOx/TiO2 catalyst for the combined abatement of NO and o-dichlorobenzene (o-DCB, model molecule to simulate PCDD/Fs) from the off-gases of a municipal waste incinerator (MWI) plant. Catalysts textural, acid and redox properties have been characterized by N2 adsorption–desorption isotherms, XRD, NH3-TPD and H2-TPR and a higher surface area, acidity and reducibility of the metal loaded zeolite catalysts have been confirmed. By catalytic tests carried out in the experimental conditions close to those employed in MWI plants, it was concluded that VOx/TiO2 show higher catalytic performance than metal/zeolite catalysts. A relationship between metal reducibility and the catalyst activity was found. However, zeolites due to their high acidity are less selective to NH3 oxidation reaction (negligible N2O formation) and therefore higher NO conversion is obtained in a wider operating temperature window. Using zeolites selectivity to CO is lower, although traces of trichlorobenze are detected. Both reactions are well fit to first order reaction kinetic over all the catalysts. In addition, neither of the catalysts show evidence of deactivation during 12h of reaction. Among metal/zeolites, Cu/Z is the most active catalyst, whereas Fe/Z is the less for both NO reduction and o-DCB oxidation reactions. Unfortunately, Cu/Z high selectivity to highly chlorinated compounds, like trichlorobenzene, was also found.