Characterization I (Molecular Sieves) by Hellmut G. Karge and Jens Weitkamp

By Hellmut G. Karge and Jens Weitkamp

Molecular Sieves - technological know-how and Technology covers, in a accomplished demeanour, the technological know-how and expertise of zeolites and all similar microporous and mesoporous fabrics. Authored by means of well known specialists, the contributions are grouped jointly topically in the sort of manner that every quantity of the e-book sequence bargains with a selected sub-field. quantity four covers the characterization of molecular sieves with the aid of crucial spectroscopic recommendations (Characterization I), i.e. IR, Raman, NMR, EPR, UV-VIS Spectroscopy, X-ray absorption, photoelectron and M?ssbauer Spectroscopy. idea, test and alertness in chosen examples are mentioned.

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In principle, Eq. (24) is valid only for dilute systems. For instance, in the case of zeolites populated with OH groups or adsorbate/zeolite systems one has to be aware of the possibility that en˜ may be dependent on the OH group concentration and adsorbate coverage, respectively. Frequently, it is sufficient to use as a first approximation the maximal absorbance defined by Eq. (26). Amax = log T* (n˜min)/log T(n˜min) (26) where T*(n˜min) is the background (base line) transmittance and T (n˜min) the actual transmittance, both measured at the wavenumber n˜min of minimal transmittance (cf.

Comparable assignments of bands at about 450 cm–1 to four-ring opening modes were suggested in investigations of spherosiloxanes [12] and of models designed to mimic the double-four-ring unit in zeolite A [10]. The drawn conclusions are also in line with the results yielded by Iyer and Singer in calculations of sodalite [118] and zeolite A [119] using a shell model potential. The authors found that many modes are localized in the four-ring, six-ring, and double-four-ring units of the framework in close resemblance for both types of zeolites.

While for organic molecules this question can easily be answered in terms of characteristic group frequencies, the answer for zeolites is not straightforward due to the complexity of zeolitic systems and the variety of framework types with diverse structural features. At first we will focus on some selected problems of framework dynamics. From the detailed comparison of abundant experimental infrared spectra in the region between 1300 and 200 cm–1, Flanigen, Khatami, and Szymanski derived a correlation between observed bands and structural features of zeolite frameworks, known since that time as the FKS correlation [112].

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