Abstract
Copper ions on over-exchanged Cu-MCM-22 were monitored by CO and NO adsorption at 300 K and NO adsorption at 77 K. Two different species of both Cu(I) and Cu(II) ions were produced by vacuum thermal treatment at 823 K. CuI-CO complexes were formed upon CO adsorption and converted to CuI-(CO)2 complexes upon increasing the CO pressure. CO adsorbed on copper ions on small oxide aggregates or in oligomeric cationic compounds was also found. Mononitrosylic CuI-NO complexes (band at 1813 cm-1) were formed upon NO adsorption and completely oxidized to CuII-NO complexes (absorptions at 1899 and 1908 cm-1) at 300 K upon increasing NO pressure. Nitro, nitrate, and nitrite species were formed by reaction of NO at 300 K with oxidic surface aggregates. Low-temperature NO adsorption experiments inhibited both the Cu(I) to Cu(II) conversion and the reactivity of the aggregates and offered clear-cut evidence of the presence of two Cu(I) sites in the MCM-22 zeolite (IZA code, MWW) structure. Besides, under higher NO pressure, mononitrosylic CuI-NO complexes transform to dinitrosylic CuI-(NO)2 complexes. Dimers of NO, as free species or bound to copper ions, were also observed and formed probably by NO confinement within the small spaces of the MWW cages at very low temperatures. The peculiar reactivity of Cu-MCM-22 under NO adsorption at 300 K suggests that this material is a potential catalyst for NOX abatement.
Lingua originale | Inglese |
---|---|
pagine (da-a) | 6875-6880 |
Numero di pagine | 6 |
Rivista | Langmuir |
Volume | 18 |
Numero di pubblicazione | 18 |
DOI | |
Stato di pubblicazione | Pubblicato - 3 set 2002 |