Framework modes

Fig. 2e), virtually absent in perfect siUcalite-1 and immediately identified as a fingerprint of TS-1 material [37,52-55,63,70,71]. A qualitative correlation between the intensity of the infrared band at 960 cm and Ti content has been observed since the first synthesis of TS-1. Indeed, the occurrence of that band is one of the distinctive features of the material cited in the original patent [7]. However, the quantitative correlation has been reported only very recently by Ricchiardi et al. [52], owing to very serious experimental problems related to the saturation of the IR framework modes, hi the same work, the nature of the 960 cm band has been discussed in terms of theoretical calculations based on both cluster and periodical approaches. 

In the early 1990s Raman spectroscopy was applied to the characterization of TS-1 catalysts [55,56]. In such experiments, beside the 960 cm band, already observed by IR spectroscopy (see Sect. 3.5), a new component at 1125 cm was detected by Scarano et al. [55] (see Fig. 2f). The 1125 cm band was recognized to be a fingerprint of the insertion of Ti atoms in the ze-olitic framework [55]. This band could not be observed in the IR studies as totally overshadowed by an extremely intense band around 1000 cm due to Si02 framework modes (Fig. 2e). 

Floyd, P.A. Leveridge, B.E. 1987. Tectonic environment of the Devonian Gramscatho basin, south Cornwaii framework mode and geochemicai evidence from turbiditic sandstones. Journal of the Geological Society of London, 144, 531-542. 

Figure 4. In situ FT-FAR-IR spectra of NIKNaZ (lower) and HNaZ (upper) for (A) zeolite A (B-B) faujasite, Si/Al=1.25, 2.5, 3.8. (F represents a framework mode, A is a supercage NH + cation mode and S are residual sodium cation modes).

The interaction between the adsorption sites of a zeolite and a probe molecule perturbs the normal vibrations of the molecule and leads to frequency shifts compared to the gas phase which can be interpreted in terms of the strength and nature of the interactions with the adsorption sites of the zeolite. INS is advantageous for observing such interactions for hydrogenous molecules [116,117]. In the infrared spectra the out-of-plane bending modes and the ring vibrations coupled with CH in-plane bending are obscured by the zeolite framework modes below 1300 em . ... 

To verify the correlation between site occupancies and far-infrared (FIR) bands, at first we have to distinguish between bands arising from cations and those originating from framework modes. This can be achieved by isotope substitution techniques. LabeHng of ZSM-5 zeoHtes with the isotopes O and yielded sig-... 

In the region between 500 and 200 cm the Raman spectra are characterized by two weaker bands at about 370 and 300 cm, slightly shifted in dependence on the kind of cation. These bands have to be assigned to faujasite framework modes. Their exact positions have been observed to be dependent on the hydration level of the sample [295]. 

Garrone E, Bonelli B, Lamberti C, Civalleri B, Rocchia M, Roy P, Otero Arean C (2002) Coupling of framework modes and adsorbate vibrations for CO2 moleculariy adsorbed on alkali ZSM-5 zeolites mid- and far-infrared spectroscopy and ab initio modeling. J Chem... 

Conceptual framework, modeing in system dynamics and fuzzy logic... 

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