Characterization of H and Cu mordenites with varying SiO_2/Al_2O_3 ratios, by optical spectroscopy, MAS NMR of ~(29)Si, ~(27)A1 and ~1H, temperature programmed desorption and catalytic activity for nitrogen oxide reduction

摘要

H-mordenites (HMor) with variable SiO_2/Al_2O_3 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 ~(27)Al, 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.