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Structure of Co Centers in BEA and MFI Zeolites. Differences in CH4- and C3H8-SCR-NOx under Presence/Absence of Water
Authors: Čapek Libor | Wichterlová Blanka | Dědeček Jiří | Kaucký D | Sobalík Zdeněk
Year: 2003
Type of publication: ostatní - přednáška nebo poster
Name of source: EuropaCat-Vi
Publisher name: University of Innsbruck, Austria
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cze
eng Structure of Co Centers in BEA and MFI Zeolites. Differences in CH4- and C3H8-SCR-NOx under Presence/Absence of Water The contribution deals with the analysis of the structure of Co centers in ZMS-5 and beta zeolites and their relation to SCR-NOx with methane and propane. The structure of Co centers has been detected by means of the characteristic bands of UV-VIS spectra of Co ions and FTIR spectra of skeletal vibrations reflecting perturbation of the framework T-O bonds due to Co ion bonding to framework, monitored at "ex-situ" and "in-situ" conditions. Two main types of Co species have been formed by ion exchange with Co nitrate and Co acetate in ZMS-5 and beta zeolites; the single Co(II) ions and defined Co-O species. Formation and location of Co species depends on the distribution of Al in the zeolite framework. Single Co ions are balanced by two Al atoms in the ring of the cationic site, while the Co-O species require presence of close but more distant Al atoms compared to the former case. For activation of methane in CH4-SCR-NOx close single Co ions are necessary, as found with Co-ZMS-5 but not with Co-beta zeolite. On the othet hand, for activation of propane in C3H8-SCR-NOx, Co-ZMS- and Co-beta are sufficiently active. Presence of water vapor, as existing in real exhaust gases, dramatically change SCR-NOx activity of Co species with respect to methane and propane. The activity of single Co ions is substantially decrreased in the presence of water vapor for both CH4- and C3H8-SCR-NOx. The stable C3H8-SCR-NOx activity was observed during 100 h at 30 000 h-1. BEA and MFI zeolites, Co centers

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