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The aim of this study was to characterize Pd catalysts supported on three different mordenite zeolites (a commercial sample and two laboratory preparations) previously tested for the NO decomposition reaction. H 2 chemisorption, TPR, FTIR spectroscopy of adsorbed CO and NO, DRS UV-vis and TPD of NO were used to characterize the catalysts. After reduction at 573 K a large fraction of Pd o particles and some Pd 2? ions were found in the commercial sample and one laboratory preparation. In contrast a sample prepared with a mordenite synthesized using a natural clay was found to exhibit mainly ionic Pd. The amount of Pd o (PdO) relative to Pd 2? depends on the oxidation temperature and the metal loading. The catalysts exhibited similar levels of activity for the NO decomposition reaction at 673 K but a different selectivity to N 2 O. This behavior was related to differences in metal dispersion and other surface conditions that influence the formation of PdO particles.

Recebido em 10/3/03; aceito em 26/9/03 NITRIC OXIDE DECOMPOSITION ON COPPER SUPPORTED ON ZEOLITES. Direct decomposition of NO on copper supported on zeolite catalysts such as MCM-22 and Beta was compared with that on the thoroughly studied Cu-ZSM-5. The catalysts were prepared by ion-exchange in basic media. They were characterized by atomic absorption, surface area, nitrogen adsorption at 77K, X-ray diffraction and temperature programmed reduction. The products of the reaction were analyzed by Fourier transform infrared spectroscopy using a gas cell. Catalytic activity tests indicated that zeolite catalysts, like Beta and MCM-22, lead to NO conversion values comparable to ZSM-5.

Palladium and/or molybdenum catalysts supported on mordenite were prepared and characterized by XRD, UV-vis, DRS, textural properties analysis, TPR, TPD and chemical analysis. The Mo-catalyst rapidly deactivated after the first minutes reaction. The Pd-catalysts were active in the NO decomposition reactions. The incorporation of Mo in the Pd-catalysts improved their catalytic properties.