Chabazite cage

These analyses and others are consistent with the occupancy of each chabazite cage by one TEA molecule, i.e. 1 TEA/12 T02.<15)... 

The absence of aromatic products appears to be related to the size of the chabazite cage which is too small to allow the formation of a benzene ring. The reaction mechanism has been established in broad outline [123-125], although many important details are still not fully understood ... 

Fig. 6. Disrupted chabazite framework of the nickel-containing precursor to the AIPO4-34. The Ni(II) complex is in the middle of the chabazite cage forming a unique P—0—Ni—O—P bridge.

A detailed discussion on the sites of important cations in zeolites A, X, Y, chabazite (cage-type with 8-oxygen ring window) and heulandite (channel-type) is given in 7.4.1. 

Water intrusion-extrusion isotherms performed at room temperature on hydrophobic pure silica chabazite show that the water-Si-CHA system displays a real spring behavior. However, Pressure/Volume differences are observed between the first and the second cycle indicating that some water molecules interact with the inorganic framework after the first intrusion. 29Si and especially H solid state NMR and powder X-ray diffraction demonstrated the creation of new defect sites upon the intrusion-extrusion of water and the existence of two kinds of water molecules trapped in the super-cage of the Si-CHA a first layer of water strongly hydrogen bonded with the silanols of the framework and a subsequent layer of liquid-like physisorbed water molecules in interaction with the first water layer. 

Figure 2 (i) Layered organization. ..abc... stacking) of the organic molecules within the chabazite-type host framework, (ii) schematic representation of the SDA s random distribution within the cages. 

The cage or window effect was proposed by Gorring (48) to explain the nonlinear effect of chain length observed in hydrocracking of various n alkanes over T zeolite, chabazite (CHA) and erionite (ERI). Thus, when a nC22 alkane is cracked over erionite, there are two maxima in the size distribution of the product molecules at carbon numbers of 4 and 11 and a minimum at carbon number of 8. The diffiisivities of n-alkanes also change in a similar periodic manner by over two orders of magnitude between the minimum at C8 and the maxima. This shows that for diffusion, and hence for shape selective effects, not only the size but also the structure of the reactant and product molecules need to be considered. 

It might be desirable to load cesium onto chabazite before mineralization. Chabazite reacts hydrothermally with aqueous cesium chloride to form pollucite, a naturally occurring mineral with cesium trapped in aluminosilicate cages. Reaction of cesium-loaded chabazite with pure water might produce pollucite or the sodium zeolite, faujasite. 

The chabazite framework has a 3-dimensional 8-ring channel system. The free aperture of the 8-ring pore opening is 3.8 x 3.8 A. Its framework contains columns of alternating D6R and CHA cages along the c direction. 

A completely different approach involves organometallic complexes with a relatively rigid structure that can be used as templates for the synthesis of zeolites. Balkus et al. showed that permethylated cobalticinium ion (CoCp2 ) can be employed to synthesize a new zeolite UTD-1, which was the first zeolite with 14-membered ring channels. The (CoCp2 ) complex was also used to synthesize ZSM-51 and AlPO-16. This zeolite and zeotype, respectively, exhibit cages into which this template nicely fits. Another example is the employment of 1 -aminoadamantane for the synthesis of chabazite. 

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