Reducao catalitica selectiva dos oxidos de azoto sobre zeolitos permutados com metais

Selective catalytic reduction of nitrogen oxides by hydrocarbons, in an oxidising atmosphere, was studied on copper exchanged zeolites. Characterisation results revealed that the catalyst Si/A1 ratio, copper content and zeolite structure influence the nature and concentration of copper species present into zeolite. The decrease of Bronsted acidity on the three types of studied catalysts (CuMFI, CuMOR and CuY), by increasing the Zeolite Si/A1 ratio or copper content or even by replacing the cocation H"+ by Na"+, leads to catalyst more active for NO SCR by propene at low temperatures. Therefore, it was concluded that Bronsted acidity does not promote NO reduction by propene. The catalytic activity of copper exchanged zeolites also depends on zeolite structure, following the order: CuMFI>CuMOR>CuY. It was further verified that not all Cu species exchanged into zeolites have equivalent catalytic activity, being the isolated Cu"2"+ ions the most active species for NO SCR by propene. The presence of water decreases the catalytic activity and deactivates the catalyst. However the catalyst deactivation extent depends on the zeolite Bronsted acidity, increasing when the Bronsted acidity increases. Furthermore, the results revealed that the catalyst deactivation is due to an alteration in copper species locationAvailable from Fundacao para a Ciencia e a Tecnologia, Servico de Informacao e Documentacao, Av. D. Carlos I, 126, 1200 Lisboa / FCT - Fundação para o Ciência e a TecnologiaSIGLEPTPortuga