Effect of sulfur dioxide on nitric oxide adsorption and decomposition on Cu-containing micro- and mesoporous molecular sieves

NO decomposition was studied at different temperatures on copper-exchanged ZSM-5, AlMCM-41 and NbMCM-41 molecular sieves. Cu-ZSM-5 zeolites presented the highest activity. SO2 poisoning was also performed and Cu-NbMCM-41 was found to be more resistant. IR results of NO and SO2 coadsorption either at room temperature or at 573 K show evidence that sulfate formation occurred at 573 K and partially prevented NO adsorption on Cu2+ in square planar structure in Cu-ZSM-5. Sulfation of Cu-NbMCM-41 was quite low due to niobium incorporated into the lattice. By contrast, niobium present in the extra-lattice position in CuNb-ZSM-5 and CuNb-AlMCM-41 did not protect the catalyst from sulfation. H-2-TPR results suggested that sulfates were formed on copper sites. IR spectra after treatment under SO2 +O-2 at 673 K indicated that sulfated species were covalently bonded, their structure varying according to the nature of the support.