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 l evels. The adsorption and surface properties have been studied using calori metry of adsorbed NO, CO, C2H4 and NH3 probe molecules. The respective numb ers and strengths of CO and NO adsorption sites on the surface, which are r elated 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 copp er species in Cu-ETS-10, and the number of Cu(I) species increased as the l evel of copper loading increased. In overexchanged Cu-ZSM-5, the Cu(I) site s were less prominent but more stable, as shown by temperature programmed r eduction (TPR) experiments. The catalytic activity for NO reduction by C2H4 in oxygen-rich atmosphere appeared to depend on the Cu(II)/Cu(I) ratio, bu t also on the adsorption properties towards the NO reactive gas. The sample s presenting the best NO adsorption properties are the most active in the N O-C2H4-O-2 reaction. (C) 2000 Elsevier Science B.V. AU rights reserved.