Zeolite membered ring channels

Small-pore zeolite Nu-6(2) has a NSI-type structure and two different types of eight-membered-ring channels with limiting dimensions of 2.4 and 3.2 A [54]. Gorgojo and coworkers developed mixed-matrix membranes using Nu-6(2) as the dispersed zeolite phase and polysulfone Udel as the continuous organic polymer phase [55]. These mixed-matrix membranes showed remarkably enhanced H2/ CH4 selectivity compared to the bare polysulfone membrane. The H2/CH4 selectivity increased from 13 for the bare polysulfone membrane to 398 for the Nu-6(2)/ polysulfone mixed-matrix membranes. This superior performance of the Nu-6(2)/ polysulfone mixed-matrix membranes is attributed to the molecular sieving role played by the selected Nu-6(2) zeoHte phase in the membranes. 

Table III lists the i-butane/n-butane ratio for cracking of n-heptane on Y and Beta zeolites with different aluminum content. The lower ratio obtained on the latter zeolite indicates that the diameter of the 12-membered ring channels of Beta zeolite must be smaller than that of Y zeolite.

Recently Briscoe et al. (2) described the framework topology of zeolite EU-1. It consists of a unidimensional 10-membered ring channel system with side pockets formed at regular intervals off the channels. The unit cell contains 112-T atoms and the framework symmetry is Cmma. 

In this part, we will summarize some of our results on the investigation of the toluene intramolecular isomerization pathways." " Both cluster approach and periodic approach methods have been employed which allow giving an illustration of the consequence of the simplistic model in the cluster approach. H-Mordenite (H-MOR) zeolite is used for the periodic calculations. The toluene molecule does not have a problem to fit within the large 12-membered ring channels of this zeolite. Furthermore, the intramolecular transition states do not suffer from steric constraints. It is known that intramolecular aromatics isomerization can proceed via two different reaction pathways (see Figure 7). The first route proceeds through a methyl shift isomerization, whereas the second route involves a dealkylation or disproportionation reaction which results in the formation of a methoxy species and benzene as intermediate. 

For the first time, a zeolite having three interconnected channel systems of different pore entrances (ITQ-22) was synthesized possessing 8-, 10 and 12-membered ring channels [39J. l,5-bis-(methylpyrrolidinium)-pentane was used as a structure-directing agent. It was found that germanium oxide controls and probably also stabilizes the formation of D4R units of this zeolite structure. 

BEA. This zeolite is characterized by large pores. There are two types of channels, small 12-membered ring channels in the [001] direction with a cross-section of 0.56 x 0.56 nm and large 12-membered ring channels in the [100] direction with a cross-section of 0.66 x 0.67 nm. In a series of... 

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. 

The aluminophosphate analog of zeolite Linde-type L (LTL) consists of 1-D 12-membered ring channels with cylindrical pore openings of 0.71 nm (35). 

Figure 21.2 Vie-w along [100] of BEA-type zeolite structure showing the 12-membered ring channel and the open Sn Lewis site.

According to the results shown in Table 1, zeolite ZSM-5, with the high Si/Al ratio 150, 10-membered ring channels and mid-strength acidity, shows both high selectivity and catalytic activity for alkylation of toluene with ethylene. 

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