Influence of the ion exchanged metal (Cu, Co, Ni and Mn) on the selective catalytic reduction of NOx over mordenite and ZSM-5

Selective catalytic reduction of NO by propene was investigated on Cu, Co, Ni and Mn ion-exchanged ZSM-5 and mordenite in the presence of excess of oxygen. The properties of the catalysts were studied by X-ray diffraction, temperature-programmed desorption/reduction and atomic absorption. H-2-TPR results showed that for copper catalysts metal was mainly present in the form of isolated Cu2+ strongly coordinated to the framework oxygen atoms of the zeolite. Cobalt, nickel and manganese were present in the form Co2+ and Co3+, Ni2+, Mn3+ and Mn4+, respectively. The catalytic activity showed for all the catalysts increased with increasing metal content reaching a maximum of NOx conversion, and then decreased at higher contents. In turn, NOx conversion increased with the reaction temperature passing through a maximum, and then decreased at higher temperatures, due to the combustion of the hydrocarbon. NO TOF for all the catalysts here prepared was analyzed at 375-425 degreesC. It was observed that this parameter decreased abruptly with the metal content and, regardless the type of zeolite and ion exchanged metal introduced in the catalysts, all the experimental points were well correlated by an unique curve. (C) 2004 Elsevier B.V. All rights reserved.