Abstract
Cu-ZSM-5 catalysts have been prepared by solid-state ion exchange at 500°C using CuCl and NH4- ZSM-5 mixture in presence of nitrogen flux. X-ray diffraction technique indicates that zeolite lattice is slightly modified for high copper loadings. The nature of copper species depends on copper exchange levels. For under exchanged catalyst, copper is mainly present as isolated Cu2+. For higher loadings, Cu+ and dispersed CuO-like species with different sizes and environments were detected besides Cu2+ ions. CuO-like species are located in the zeolite channels such as Cu2+-O-Cu2+ dimers or on the surface of zeolite crystals. Copper oxide clusters are not detectable by XRD technique, which indicates that they are amorphous and/or well dispersed on the external surface of the zeolite. The prepared catalysts show good activity in the selective catalytic reduction of NO by n-decane in oxidizing atmosphere independently of copper exchange level. The increase of copper content has an effect on the operating temperature window by decreasing the temperature of maximum NO conversion and total n-C10H22 oxidation. The presence of 25 ppm of SO2 in the reaction feed has a slight inhibiting effect for all catalysts excepting Cu(136)-Z for which NO conversion was enhanced in the temperature range of 320-425 °C.