Mordenite structure

Figure 1. Molecular graphics representations of [A] S 2 attack of a methanol molecule on a methyl oxonium ion in the side-pocket of the mordenite structure and [B] the size limitation of the bulky isobutanol molecule that prevents it from turning in the main channel to react with the methyl oxonium ion in the side-pocket.

The monometallic Pt pre-semed two inardina in the low toqrera-tures region (194 and 269°C) and a sharper peak at 560°C. This type of TPRproffle could be attributed to Pt exchanged at different sites in the 5. Effect of water addition on the NO (B) mordenite structure. The consump-... 

Many mineral and synthetic samples examined by Bennett and Gard 17,18) gave typical C-centered orthorhombic diffraction patterns and with few exceptions had streaks in the hOl section, indicating an incomplete c-glide plane. A few crystals gave electron diffraction patterns having diffuse maxima in the hOl streaks, which could be interpreted as representing an I-centered mordenite structure. 

These are the first observations of intergrowths in the Cmcm mordenite structure. They show, in the first case, that the Cmmm structure exists as discrete regions intergrown with the usual Cmcm structure while in the second, the body-centered structures only exist as very narrow regions or stacking faults. An intergrowrth of cither Cmmm or Immm and the Cmcm structure would also account for the incompleteness of the c-glide plane observed in some of the previous studies. 

Although boron cannot successfully compete with aluminum for sites in the mordenite structure, the more siliceous products contain significant amounts of boron. Figure 2 shows the B2O3 content of the products as a function of the Si02/Al203 ratio in the gel and in the product. It is clear that if enough aluminum is available in the gel to form an... 

Mordenite has a channel-like pore structure in which the basic building blocks consist of five-membered rings. A view of the mordenite structure perpendicular to the main channels is shown in Fig. 3. 

Fig. 3. Section through the mordenite structure (Z) perpendicular to the main channels. (Reproduced from Ref. 2 with permission from the author and Elsevier Scientific Publishing Company, Amsterdam.)...

The availability of such a new site would most likely be the consequence of the mordenite structure undergoing a crystal lattice expansion, opening the 8-membered ring side pocket for adsorption. 

The situation is somewhat more complicated in the mordenite structure. There are four crystallographically different T and ten O atoms. 01, 02, 03 and 04 are bonded to two crystallographically different tetrahedral atoms (Tl-... 

Assignment of the peaks on the basis of the correlation between Si chemical shifts and the mean Si-O-Si bond angle is not possible in this case. The 2D J-scaled COSY spectrum of highly siliceous mordenite reveals three cross-peaks. On the basis of the known cotmectivities of the mordenite structure, only two cross-peaks are predicted for the T1 T4 T2 + T3 assignment, while the T1 T3 T2 + T4 assigtunent implies that three cross-peaks should be observed. Thus the detection of three cross-peaks in the 2D J-scaled COSY experiment shows that the correct interpretation is T1 T3 T2 + T4. Such unambiguous assignment of the spectrum is not possible by one-dimensional NMR or by conventional COSY (15). 

I restrict my attention here to work that has applied periodic DFT calculations to structure or reactivity of zeolites. The great majority of work on this topic has focused on a small number of materials that have small unit cells, including chabazite (structure code CHA), which has 36 framework atoms per unit cell, mordenite (structure code MOR), which has 146 atoms per unit cell, ZSM-22 (structure code TON), with 72 atoms per unit cell, and ferrierite (structure code FER), with 108 atoms per unit cell. Notably, this list does not include ZSM-5, a material with 288 framework atoms per unit cell, which is the... 

Structural characterization of the solids by X-ray diffraction showed that the materials ZSM-5 and USY zeolites studied had a high crystallinity, while a mordenite structure was observed for the natural zeolite traces of clinoptilolite were observed in this sample. 

Table 2 shows the results of ethylene diffusivity values together with NOx conversion for the different H-mordenites studied in this work. Note that while D/R2 decreases an order of magnitude in the deactivated sample (if compared with the fresh one), it remains approximately constant for the samples subjected to acidic dealumination. This result suggests that the aluminum extracted from the lattice of the mordenite during of the mordenitic structure along the for the deactivation observed in the... 

It has been shown that the H-mordenite catalytic activity during the SCR of NOx with methane in the presence of oxygen excess depends not only on the total amount of framework-aluminum but also on the distribution of amorphous residuals inside the mordenitic structure. i29Xe-NMR of physisorbed Xenon and diffiision meeisurements by ZLC Chromatography were useful tools in determining this distribution in acid dealuminated H-mordenites and in the same catalysts deactivated on-stream during the SCR of NOx-... 

Fig. 5. Cross section of mordenite structure. From Meier (13. ...

Surface area measurements and pore volume confirm that the mordenite structure is not affected during the calcination treatment. 

Table 2 Connectivities and Typical Mean T-O-T Bond Angles in the Mordenite Structure [61]...

Such results have already been interpreted in terms of molecular sieve effects, due to the constrained environment in the channels of the mordenite structure [15,16]. 

This work deals with the study of the coke formation on H-mordenite during the benzene transalkylation with C9 aromatics, under several reaction conditions, in order to evaluate the condition which results in the lowest catalyst deactivation for industrial purposes. It was found that coke was produced in all samples but it was maintained around 4% (weight) without damage to activity and selectivity to toluene and xylenes. The coke was hydrogenated and could be easily removed. The soluble coke was mostly constituted by aliphatic hydrocarbons, while the insoluble coke was amorphous. These results were explained by the mordenite structure as well as by the presence of hydrogen. The best condition to perform the reaction depends much more on the selectivity to toluene and xylenes rather than on coke production. 

As was shown by Hadjiivanov [780], the adsorption of NO-1-O2 leads to the formation of NO+, which can be used as a probe for the location of OH groups [781 ]. Thus, co-adsorption of NO and O2 into mordenite produced two separate bands of NO+, a band at 2168 cm due to the interaction with OH groups in the main channels and a second one at 2215 cm, indicating the acid hydroxy groups in the side pockets. From the ratio of the intensities of these bands (2 1), the authors concluded that the population of the main channels with OH groups is twice as that in the side pockets (see, however, above and cf. [477]). When Na cations were present in the mordenite structure, nitrate was formed and indicated by intense nitrate bands. The situation was more complicated when not only B-... 

Figure 2.11 The structure of the gallosilicate TNU-7 (and the aluminosilicate ECR-1), shown below, projected down the large channels, can be thought of as being built up from strictly alternating sheets maz and mot) that are found in the mazzite and mordenite structures, shown above left and right, respectively.

---