Erionite ERI , Offretite OFF

IR framework spectra were used as a diagnostic tool by Occelli et al. [260] in detecting the presence of offretite (via a band at 600-610 cm ) and erionite (bands at 410-425,550-610,655-685 cm ) in mixtures of these two structures. Roessner et al. [261 ] considered, in their IR spectroscopic work on the cation distribution in dehydrated calcium-exchanged erionite, also the framework vibrations of Ca-erionite besides OD vibrations, CO adsorption and DRIFT spectroscopy in the NIR region. They were able to show that the Ca + cations were selectively located in the supercages in front of the six-membered rings. Similar to the features encountered with Y-type zeolites and mordenite (vide supra), also with offretite a sufficiently linear relationship was found between the wave-numbers of the asymmetric and symmetric T-0 vibrations and the number of framework Al atoms per unit cell [262]. 

Framework spectra of zeolite K-L were reported by Tsitsishvili [203] and related to the data of Flanigen et al. [112]. Also, IR spectroscopic features of water adsorbed on K-L (vide infra) were included in Ref. [203] (see also [252]). Dealu-mination of zeolite L via various methods was also studied (cf., e.g.. Sect. 5.4.1.2.2) 

Samples of zeolite Beta with various degrees of dealumination were prepared via various treatments by Yang and Xu [263]. These authors provided framework spectra of their samples, obtained in the region 1400-400 cm through the conventional FTIR/KBr pellet technique. A band at about 950 cm was attributed to Si-O vibrations in structural vacancies (cf. also [264]) and monitored in dependence on the treatment. 

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