| Article ID | Journal | Published Year | Pages | File Type |
|---|---|---|---|---|
| 41643 | Applied Catalysis A: General | 2011 | 10 Pages |
The structure, properties and activity of the counter Co, Cu and Fe ion species depending on the distribution of aluminium atoms in the framework between Al pairs of Al–O–(Si–O)2–Al sequences in one ring and isolated Al atoms (Al–O–(Si–O)n>2–Al sequences) in two rings are analyzed. The effect of the Al distribution on the activity of metal ion species is investigated for reactions of technology importance, i.e. SCR-NOx by propane, and decomposition of NO and N2O under real conditions of NOx streams. Zeolite samples of BEA, MFI and FER structures, of similar composition for each topology, but with basically different distribution of Al atoms in the framework, were either selected from commercial samples or prepared by the developed synthesis. The concentration of Al pairs and isolated Al atoms in the framework was determined by the combination of 29Si MAS NMR and quantitative analysis of the Vis spectra of dehydrated Co-zeolites with Co(II) ions exchanged to a maximum degree. The structure and reactivity of the metal sites was described by UV–Vis, FTIR of skeletal vibrations and adsorbed NO, TPR-H2 and reactions of C3H8-SCR-NOx/H2O, and NO and N2O decomposition. It is concluded that the local negative framework charge, originated from Al pairs and isolated Al atoms, constitutes a decisive parameter controlling the structure and reactivity of the counter metal ion species. The bare Co(II), Cu(II) and Fe(II) ions are balanced by Al pairs, while Co-oxo and Cu-oxo or Cu(I) species are adjacent to isolated Al atoms. The Cu(I) ions in vicinity of isolated Al atoms in Cu-MFI zeolites are the most active sites in NO decomposition. Co-oxo species attached to isolated Al atoms in Co-BEA zeolites, in contrast to bare Co(II) ions, exhibit high activity in C3H8-SCR-NOx/H2O in the presence of water vapor. N2O decomposition to elements over Fe-FER requires two Fe ions at a defined distance of β cationic sites, with each Fe(II) cation charge-balanced by an Al pair.
Graphical abstractIsolated Al and Al pairs in the framework decisively control the structure, properties and activity of the counter Co, Cu and Fe species in Co-BEA, Cu-MFI and Fe-FER catalysts. This enables to tailor the catalyst structures for reactions of technology importance: C3H8-SCR-NOx and decomposition of NO and N2O under real conditions of wet NOx streams.Figure optionsDownload full-size imageDownload high-quality image (27 K)Download as PowerPoint slideResearch highlights▶ Distribution of aluminium atoms in the framework controls structure and activity of metallo-zeolites. ▶ Divalent bare cations balanced by Al pairs and metal-oxo species balanced by isolated Al atoms exhibit dramatically different redox behavior. ▶ Co-oxo species in BEA balanced by isolated Al atoms are active in C3H8-SCR-NOx under excess of water vapor. ▶ Two Fe ions in FER, each balanced by an Al pair and located at opposite cationic sites are active in N2O decomposition. ▶ Cu ions charge-balanced by isolated Al atoms and readily reduced are centers for NO decomposition.
