NO decomposition over Cu-Sm-ZSM-5 zeolites containing low-exchanged copper

Catalysts were prepared by exchange and co-exchange techniques following Iw amoto's procedure. Copper-exchange degree in the zeolites varied between 21 .2% and 128% while the Sm content varied in inverse order, between 27.2% an d 18.8%. The catalysts were characterized by NO-DRIFT, O-2-TPD, and XPS. Ca talytic tests were performed in a microreactor in the temperature range 673 -873 K. It was found that the presence of Cu in close proximity of the Al f ramework, i.e., in the exchangeable positions, is increased in the presence of Sm. The presence of Sm stabilizes the Cu(I)-O-Cu(II) "redox buffer," in creasing the activity of this catalyst. This behavior is mainly observable for low Sm concentration. (C) 2000 Academic Press.