Characterization of copper-exchanged ZSM-5 and ETS-10 catalysts with low and high degrees of exchange

Two different copper molecular sieve systems (Cu-ZSM-5 and Cu-ETS-10) have been prepared with different copper loadings from under- to overexchanged levels. The adsorption and surface properties have been studied using calorimetry of adsorbed NO, CO, C2H4 and NH3 probe molecules. The respective numbers and strengths of CO and NO adsorption sites on the surface, which are related to the ratio of Cu(I) to Cu(II), depend on the matrix type, location of the metal ions, and degree of Cu exchange. Cu(I) was the prominent copper species in Cu-ETS-10, and the number of Cu(I) species increased as the level of copper loading increased. In overexchanged Cu-ZSM-5, the Cu(I) sites were less prominent but more stable, as shown by temperature programmed reduction (TPR) experiments. The catalytic activity for NO reduction by C2H4 in oxygen-rich atmosphere appeared to depend on the Cu(II)/Cu(I) ratio, but also on the adsorption properties towards the NO reactive gas. The samples presenting the best NO adsorption properties are the most active in the NO-C2H4-O2 reaction. (C) 2000 Elsevier Science B.V. All rights reserved.