Catalytic activity of Cu-offretite catalysts prepared by solid state ion exchange in the reduction of NO with NH3

Abstract

Cu-OFF catalysts with different copper loadings, prepared by solid state ion exchange, were characterized by UV-visible reflectance spectroscopy, H 2-TPR, NH3-TPD, 27Al MAS NMR and tested for selective catalytic reduction of NO by ammonia in presence of oxygen. At low Cu content (exchange level < 40 %), TPR profiles show the presence of two peaks of comparable areas, suggesting that Cu2+ remain isolated and are reduced in two successive steps: Cu2+ → Cu+ at about 220°C and Cu+ →Cu0 at 800-850°C. At higher Cu content, the TPR profiles are modified with a large increase of the low temperature peak with depends of the high temperature peak, thus suggesting the formation of Cu oxide clusters in the lattice of offretite. The acidity of the offretite also decreases upon exchange. The NO reduction activity is proportional to the number of Cu2+ ions up to 40 % exchange, then decreases. Isolated Cu2+ ions appear then more active than CuO clusters for the selective reduction of NO by NH3. © 2005 Elsevier B.V. All rights reserved.