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. H₂-TPR results suggested that sulfates were formed on copper sites. IR spectra after treatment under SO₂ + O₂ at 673 K indicated that sulfated species were covalently bonded, their structure varying according to the nature of the support. This revised version was published online in August 2006 with corrections to the Cover Date.