NO decomposition over physical mixtures of Cu-ZSM-5 with zeolites or oxides

The paper deals with the investigation of the activity of bicomponent Cu-M-ZSM-5 zeolites (M = Ce, Sn, TI) and of the physical mixtures of Cu-ZSM-5 with M-ZSM-5 or with the corresponding oxides of these metals in NO decomposition. Physical mixtures of M-ZSM-5 with those corresponding oxides were investigated as well. Copper exchange degree in the zeolites varied between 21.2 and 128% while the M content varied in inverse order, between 27.2 and 18.8%. The catalysts were characterized by NO-DRIFT, O-2-TPD and XPS. Catalytic tests were performed in a microreactor in the temperature range 673-873 K. It was found that the presence of a second component may indeed lead to a better positioning of Cu, resulting in an improvement of its catalytic properties. This effect is conditioned by the introduction of M together with Cu in the exchange solution. Physical mixtures of Cu-ZSM-5 with M-ZSM-5 or with M oxides are not effective, confirming the importance of the co-exchange. The chemical nature of M is a key factor in this process. (C) 2001 Elsevier Science B.V. All rights reserved.