Alkali-metal cation-exchanged faujasites

I.A. Beta, H. Jobic, E. Geidel, H. Bohlig B. Hunger (2001). Spectrochim. Acta A, 57, 1393-1403. Inelastic neutron scattering and infrared spectroscopic study of furan adsorption on alkali-metal cation-exchanged faujasites. 

H. FSrster, H. Fuess, E. Geidel, B. Hunger, H. Jobic, C. Kirschhock, O. Klepel K. Krause (1999). Phys. Chem. Chem. Phys., 1, 593-603. Adsorption of pyrrole derivatives in alkali metal cation-exchanged faujasites comparative studies by surface vibrational techniques. X-ray diffraction and temperature-programmed desorption augmented with theoretical studies Part I. Pyrrole as probe molecule. 

WAVENUMBER [cm ] Fig. 1S. Far-infrared (FIR) spectra of alkali-metal cation-exchanged faujasites and H-Y zeolite... 

It can be seen in Fig. 15 that within the series of alkali-metal cation-exchanged faujasites the bands are shifted to lower wavenumbers with increasing cation mass. This phenomenon was recognized very early by Brodskii et al. [358,359]. In an attempt to correlate the observed band positions with physical characteristics of the cations they found the relation... 

The situation is entirely different when alkali metal cation exchanged zeolites of faujasites are used. The conversions are high and the selectivity to NMA is high. This is due to the reduction in acidic centres and increase in the basic sites. The consequence of such reduction is the suppression of successive alkylations and disproportionation reactions. 

The protons released are presumably available to compensate for the loss of the charge balancing cations within the zeolite. In conventional syntheses, the phtha-lonitrile condensation normally requires the nucleophilic attack of a strong base on the phthalonitrile cyano group [176, 177]. This function is presumably accommodated by the Si-O-Al (cation) basic sites within the ion-exchanged faujasite zeolites [178, 179]. The importance of this role is perhaps emphasized by the widespread use of alkali metal exchanged faujasites, particularly the more basic NaX materials of higher aluminium content [180, 181] as hosts for encapsulated phthalocyanine complexes. 

Impregnation followed by thermal treatment is commonly used to prepare alkali metal oxide or alkaline earth metal oxide clusters in molecular sieves in order to obtain catalysts with basic properties. A first hint at the usefulness of such procedures was published in 1984 Lacroix et al. reported that cesium-exchanged zeolite X is more active in the side-chain alkylation of toluene with methanol when left unwashed after the cation exchange [1]. Hathaway and Davis [2-4] carried out further systematic studies on the preparation of intrazeoUtic oxide clusters with basic properties. These authors described two methods for the introduction of alkali metal oxides into the pores of faujasites [2j When zeolites X and Y, ion-exchanged at room temperature with aqueous solutions of alkali metal acetates or... 

The structure of and possible cation location in these materials is fairly well known (2, 8, 4, )> and their ion-exchange behavior toward a multitude of pairs of ions, mostly including sodium, has been measured and interpreted in terms of basic properties of ions, crystal structures, and pore dimensions. The major part of these studies is with alkali- and alkaline-earth cations, alkylammonium ions, rare-earth cations, and silver and thallium ions (1). In contrast, the ion adsorption of transition metals in faujasite has received little attention. 

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