Infrared Spectroscopy Characterization of Zeolitic Systems

Infrared Spectroscopy Characterization of Zeolitic Systems 129 Bronsted Acid Site Distribution... 

Zeolites. The weak Raman signals arising from the aluminosilicate zeolite framework allow for the detection of vibrational bands of adsorbates, especially below 1200 cm which are not readily accessible to infrared absorption techniques. Raman spectroscopy is an extremely effective characterization method when two or more colored species coexist on the surface, since the spectrum of one of the species may be enhanced selectively by a careful choice of the exciting line. A wide range of adsorbate/zeolite systems have been examined by Raman spectroscopy and include SO2, NO2, acety-lene/polyacetylene, dimethylacetylene, benzene, pyridine, pyrazine, cyclopropane, and halogens. Extensive discussions of these absorbate/zeolite studies are found in a review article by Bartlett and Cooney. ... 

Application of Raman spectroscopy to zeolite research was, for a long time, hampered by severe problems due to fluorescence phenomena. These could be overcome during the recent past (cf. Sect. 4.4 and [229]). Meanwhile, IR and Raman results of zeolite investigation, as reported in the literature are so muner-ous that an exhaustive overview would be beyond the frame of the present chapter [compare, therefore, also earlier reviews such as those by Yates [230], Ward [231], Baker et al. [232] (especially for Fourier transform far-infrared spectroscopy), Foerster [233] and Karge et al. [234]. However, in the following subsections many examples will be provided which are meant to demonstrate the high potential of IR, Raman spectroscopy and INS for the characterization of zeofites and related systems. 

With the advent of sohd-state NMR, another powerfiil tool for the characterization of zeohtes and related materials emerged. Similarly and, in many respects, complementarily to infrared spectroscopy, solid-state NMR spectroscopy enabled investigations to be carried out of the zeolite framework, extra-frame-work cations, hydroxyl groups in zeolites, pore structure, and zeolite/adsorbate systems. The contributions of solid-state NMR to molecular sieves research is reviewed by M. Hunger and E. Brunner in Chapter 2. 

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