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FTIR Study of CO Interactions with Li + Ions in Micro- and Mesoporous Matrices: Coordination and Localization of Li + Ions

2007; American Chemical Society; Volume: 111; Issue: 30 Linguagem: Inglês

10.1021/jp0716785

1932-7455

Petr Nachtigall, Karel Frolich, Helena Drobná, Ota Bludský, Dana Nachtigallová, Roman Bulánek,

Chemical Synthesis and Characterization

The interaction of CO with extraframework Li+ ions coordinated in ZSM-5 and FER zeolites with different compositions is investigated by FTIR spectroscopy, and the correlation between Li+ coordination, stability of CO adsorption complexes, and νCO frequencies is discussed in terms of the theoretical investigation of the stability and vibrational dynamics of CO adsorption complexes. Differences in IR spectra of adsorbed CO due to the following effects were considered: (i) various Si/Al ratios, (ii) differences in zeolite topology, (iii) temperature, and (iv) the effect of a co-cation on relative stability and metal cation site preferences. The correlation between Li+ coordination and νCO frequencies of CO adsorption complexes discussed for Li zeolites is extrapolated to mesoporous Li−(Al)MCM-41 materials. The features in the IR spectra of CO/Li−(Al)MCM-41 are assigned to CO adsorption complexes formed on top of five- and six-membered rings on the surface of a channel wall. The spectra of CO/Li−ZSM-5 with different Si/Al ratios and various ion exchange levels bring evidence on the nonstatistical distribution of aluminum in the framework and on the preference of Li+ ions for channel-wall sites.