Characterization of H and Cu mordenites with varying SiO₂/Al₂O₃ ratios, by optical spectroscopy, MAS NMR of ²⁹Si, ²⁷Al and ¹H, temperature programmed desorption and catalytic activity for nitrogen oxide reduction

H-mordenites (HMor) with variable SiO₂/Al₂O₃ molar ratio (MR) varying from 10 to 206 were incorporated with copper (CuMor). Maximum total acidity and maximum concentration of the strongest acid sites were found for MR=15 (HMor15). This sample has the lowest micropore and mesopore content, but also show strongly disordered Si sites in the crystalline lattice. A consistent finding has been the disappearance of the NMR line from extra- framework ²⁷Al, whenever Cu is present. The reducibility of copper ions and stability of reduced species depend on MR. The MR also influences optical lineshapes from different reduced species of Cu. A plasmon resonance band at 580 nm, due to small Cu particles formed in the zeolite, occurs at low and high MR but not at MR=15. Catalytic tests of NO conversion reveal that the reduced Cu-mordenites with MR=15 are the most stable and active ones.