Zeolite MOR

Sachtler and coworkers showed evidence of CO adsorption on monoatomic Pt with a CO vibrational frequency at 2123cm Hn H-MOR zeolite [142]. This band is shifted to significantly higher frequencies than the -2070 cm band that is typically observed for CO on multiatomic clusters. They proposed that these electron-... 

Anisole and veratrole acetylation with AA were carried out over three large pore zeolites HFAU, HBEA and HMOR and one average pore size zeolite HMFI.[3] With both substrates, the initial rates as well as the maximum yield were found lower over the monodimensional MOR zeolite and with MFI, which was explained by diffusion limitations. Anisole acetylation was shown to be quicker and the maximum yield higher over HBEA than over HFAU, whereas the reverse was found with veratrole acetylation.[3,4] Such behaviour could be explained from the relative sizes of the acetylation intermediates and of the micropores (transition shape selectivity).[3] Whereas HFAU and HBEA zeolites with similar Si/Al ratios have practically the same activity for 2-MN acetylation, HMFI is practically inactive. Furthermore, HBEA is more active than HFAU for 1-AMN isomerization. 

Cerqueira and co-workers203 confirmed the appearance of the of the tetrahedral aluminium and phosphorus in AlPO-like crystalline structures both in beta (BEA) and in MOR zeolites treated with phosphoric acid. 31P MAS,27Al MAS and TQM AS NMR spectra permitted the species present in the samples to be assigned. Possibly, besides the the Altet-f species, other Al species are also taking part in the activity and selectivity of the catalysts. The formation of Alocl o P can also contribute to the increase in the activity by preventing further dealumination. Dual zeolite additives have no impact on the quality of naphtha when compared to MFI-based additives, which are used in the fluid catalytic cracking processes. 

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. 

Similarly, Co ions at the external surface of Co-H-FER and Co-H-MOR have been detected. Similar experiments with hindered nitriles show the location of alkali ions at the external surface ofalkali-MOR zeolites [160]. CO mainly adsorbs at the external surface of the small pore zeolite 3A (K-LTA) while it enters the cavities of zeolite 4A (Na-LTA) [161]. 

Figure 3. Difference of infrared spectra obtained with and without adsorbed thiophene for MOR zeolites at 1 mbar thiophene equilibrium pressure and the difference spectrum for the spent HMOR sample.

Mordenite (MOR) zeolite, a bidimensional material, also has two interconnecting channels the larger one is 6.5 x 7.0 A, whereas the second one is too small to accommodate organic molecules. 

AC is tested in the comparative acylation of 2-MN over BEA, Y, and MOR zeolites. All the three catalysts show about 30%-40% conversion of 2-MN in sulfolane in fhe femperature range 100°C-150°C. At 100°C, Y shows higher activity than the other two catalysts. However, as the reaction temperature is raised to 150°C, the initial high conversion drops rapidly, indicating faster deacylation of the primary product 28. BEA and MOR zeolites also show some deacylation at higher temperatures, but the drop in conversion is not as sharp as that observed with Y. At 150°C, yields of isomer 29 are found to be similar with all three catalysts (70%-80%) due to the faster isomerization of compound 28 to fhe fhermodynamically more favored isomer 29. 

Table 4.11 Comparison of the activity and selectivity of ZSM-5 and MOR zeolites in the gas-phase acylation of benzene with AAC at 250°C...

Due to their particular catalytic properties, iron- and iron-aluminium-substituted zeolites are especially interesting for application in oxidation processes. In this paper the preparation procedure and the adsorption properties of Fe-Al-BEA and Fe-Al-MOR zeolites are described and the results are compared with the data obtained for the corresponding aluminium forms of both zeolites. 

Similarly to the MOR zeolite, also the BEA type zeolite presents an aluminium incorporation not depending on the iron amount in the hydrogel. A decrease in A1 incorporation was observed for the iron samples compared to the iron-free sample (samples B2—B4). The iron content in the BEA crystals increases with the... 

The unchanging amount of A1 in the zeolite MOR samples indicates that the isomorphous substitution of the Fe cations takes place at the expenses of the framework Si. Most likely, the observed pore expansion of the Al-Fe-MOR zeolite, demonstrated from the data of Fig. 1, is due by the substitution of the longer Fe-0 bond (1.84 A) in the place of the Si-O bond (1.61 A). 

A further indirect support to Fe incorporation in both BEA and MOR zeolites is that after calcination at 750 °C the relevant samples exhibited a white colour. If iron had not been in the zeolitic structiure the samples would have become brown after thermal treatment. 

The use of iron oxalate complex is a good way for the preparation of Al-Fe-BEA and Al-Fe-MOR zeolites. The limit of the described procedure is that it is... 

The presence of iron increases the adsorption capacity of both BEA and MOR zeolites. In the case of MOR type zeolite all samples obtained with this procedure show a large pore channel system, larger than the commercial H-Zeolon, used as a reference mordenite. 

The desilication process of mordenite was also evaluated by FTIR spectroscopy [lOPlJ. A shift of lattice vibration bands toward smaller wave numbers was shown upon alkaline treatment. Consequently, this evolution can be taken as evidence of the silicon removal. A linear correlation between the number of framework Si per unit cell, Nsi, and the asymmetric stretching wave nmnber, Vi, was observed vi [cm ] = 20.2 Nsi+ 193.0 [lOPl], The desilicated samples exhibit the same acidic properties as the parent H-MOR zeolite. 

The surface acidity of three commercial mordenite (MOR) zeolites with Si/Al ratios of 10, 60, and 80 has been evaluated by adsorption micro calorimetry at 423 K, using pyridine as a probe molecule [210]. As could be expected from the Si/Al ratios, the total pyridine uptakes varied in the order MOR-10 >MOR-60 >MOR-80. The initial differential heats of adsorption were in the range 215-220 kJ mol After a sudden drop, Qdiff changed slightly and stepwise over a relatively wide range of pyridine uptake (at least for MOR-10) and then steeply decreased. The site-energy distributions and the thermokinetic parameters versus coverage were also determined [210]. 

Niu and Hofmann [ 164] related the activity of USY, H-ZSM-5, and H-MOR zeolite catalysts in ethylbenzene conversion to the acidity measured by IR spectroscopy using pyridine adsorption and TPD of NH3. Catalytic measurements at 300 °C did not show deactivation over all three catalysts, while increasing the reaction temperature to 400 °C led to a strong deactivation for H-MOR and some deactivation of USY. The conversion over H-ZSM-5 was not affected by deactivation. At 300 °C only disproportionation reactions were observed, while at 400 °C large contributions of cracking were found (i.e., benzene to diethylbenzene ratios above 1) over all three catalysts. 

Figure 9.6 MAS NMR spectrum of NH4-MOR zeolite (a), y-Al203 (b), and silica-alumina (c) (Courtesy Prof. S. Caldarelli [Marseille].)...

Figure 9.12 FTIR spectra of H-MOR zeolite after activation at 673 K (a) and after saturation with nitrile vapors (b) propionitrile. (c) Isobutironitrile, (d) pivalonitrile, and (e) diphenylpropionitrile...

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