MFI-type zeolite

Preparation of Mono-Dispersed MFI-type Zeolite Nanoerystals via Hydrothermal Synthesis in a Water/Surfactant/Oil Solution... 

The variation in the lattice vibration of the solid products was examined by utilizing the FT-IR technique at successive DGC process times and the results are presented in Fig. 5. The absorption bands at 550 cm and 450 cm" are assigned to the vibration of the MFI-type zeolite and the internal vibration of tetrahedral inorganic atoms. The band 960 cm" has been assigned to the 0-Si stretching vibration associated with the incorporation of titanium species into silica lattice [4], This indicates that the amorphous wall of Ti-MCM-41 was transformed into the TS-1 structure. 

The reaction mechanism of SCR of NOx with decane on acid and iron-exchanged MFI-type zeolite was also investigated by operando FTIR spectroscopy and a special reactor cell enabling the use of water-containing gas mixtures. Brosius et al. found that water has a dramatic influence on the reaction pathway, while the formation of organic nitro and nitrite compounds does not proceed via chemisorbed states of NO, as observed in SCR with dry gases [174],... 

Brosius, R., Bazin, P., Thibault-Starzyk, F. et al., (2005) Operando FTIR study of reaction pathways of selective catalytic reduction of NOx with decane in the presence of water on iron-exchanged MFI-type zeolite, J. Catal., 234, 191. 

The zeolite ZSM-5 has the MFI-type structure and can be obtained with many different Si/Al ratios typically ranging from about 10 to If no aluminum is present (Si/Al = ), a pure siliceous structure is obtained and the resulting material is then called Silicalite-1. The unit cell composition of an MFI-type zeolite can be written as (Na+, H A Si, xOl92-/ H20 withx < 27 (in most cases <9) and n < 16 (the more siliceous a zeolite gets, the higher is its hydrophobicity). 

Figure 4.31 SEM image of MFI-type zeolite, (distance between points of size bar = 50 pm total length 500 pm.)...

Guo, G. and Long, Y. (2001) Static equilibrium studies on separation of dichlorobenzene isomers on binder-free hydrophobic adsorlaent of MFI type zeolite. Sep. Purif. Technol,... 

There are many different zeolite structures but only a few have been studied extensively for membrane applications. Table 10.1 lists some of these structures and their basic properties. One of the most critical selection criterion when choosing a zeolite for a particular application is the pore size exhibited by the material. Figure 10.1 compares the effective pore size of the different zeolitic materials with various molecule kinetic diameters. Because the pores of zeolites are not perfectly circular each zeolite type is represented by a shaded area that indicates the range of molecules that may stiU enter the pore network, even if they diffuse with difficulty. By far the most common membrane material studied is MFI-type zeolite (ZSM-5, Al-free siUcahte-l) due to ease of preparation, control of microstructure and versatility of applications [7]. 

Another recent modification to the secondary growth method as applied to MFI-type zeolite membranes is to perform the hydrothermal growth on the seeded... 

Figure 10.3 SEM cross-section image and XRD spectrum fore-oriented (a), h,0,h-oriented (b), and random (template-free) (c) MFI-type zeolite membranes along with associated XRD patterns (d, e, f) [12],...

For high-quality MFI-type zeolite membranes either Knudsen or configurational diffusion is representative of the flow. Knudsen diffusion occurs in pores where... 

Figure 10.6 Temperature dependency of gas permeances for unmodified MFI-type zeolite membrane (closed symbols on solid line gas permeances for single permeation, open...

O Brien-Abraham, J., Kanezashi, M., and tin, Y.S. (2007) A comparative smdy on permeation and mechanical properties of random and oriented MFI-type zeolite membranes, Mesop. Microp. Mater., 105, 140-148. 

Kanezashi, M. and lin, Y.S. (2009) Gas permeation and diffusion characteristics of MFI-type zeolite membranes at high temperatures. J. Chem. Phys. C, 113, 3767-3774. 

MFI-type zeolite membranes. Micropor. Mesopor. Mater., 43, 319-327. 

Attempts were made to investigate the relaxivity enhancement produced by an MFI-type zeolite with framework-incorporated gadolinium (84). A relaxivity less than 3 s mM was found at room temperature and at 40 MHz. This indicates that the accessibility of gadolinium to water plays a very important role, and that the outer sphere effect might be very small. 

It was reported independently by three research groups that MFI-type zeolites selectively catalyze the reaction of N20 with benzene to give phenol C6H6 + N20 —> C6H5OH + N2 [93-96]. Fe/ZSM-5 shows remarkable performance in benzene hydroxylation to phenol with N20 as oxidant, which is the first example of a successful gas phase direct phenol synthesis from benzene [97]. No other catalysts show similar high performances to the Fe/ZSM-5 catalyst. At present, iron is the sole element capable of catalyzing the benzene-to-phenol reaction [98]. Direct oxidation of benzene to phenol by N20 has been commercialized in the so-called AlphOx process in Solutia Inc., US A, where N20 is obtained as a by-product in adipic acid production with nitric acid [97, 99, 100] a selectivity >95% to phenol is achieved at >40% conversion at around 4000 C. But the process is cost-effective only if N20 can be obtained cheaply as a by-product in adipic acid production. 

Other larger zeolites of the FAU type are used in the cracking of long-chain waxes and paraffins, which are of low value because of their viscosity. The products of this process are gasoline and liquid petroleum gas, which is treated further with MFI-type zeolites as detailed above (Figure 9.11c). 

Figure 4.11 Computer simulation of the MFI-type zeolite H-ZSM5 (left), and scheme showing the shape-selective formation ofp-xylene inthecage (right).Thanks to Dr. Edith Beerdsen forthe simulation snapshot.

Figure6.4 Simulated structure ofthe MFI-type zeolite Silicalite-1 (O atoms in dark gray and Si atoms light gray), projected on the be plane and showing the zigzag channels. The broken lines indicate the periodic cell boundaries. Alkane molecules (not drawn to scale) are indicated by black circles. Thanks to Dr. Merijn Schenk for the zeolite picture.

For these reasons we have come to the tentative conclusion that the D5R silicate condensation mechanism is not generally operative in the synthesis of MFI-type zeolites. 

Table T. Influence cf the F/Si ratio and teaperature on the Si/41 ratio in the MFI-type zeolites...

The favorable influence of organic molecules in the synthesis of MFI-type zeolites is widely recognized. For example. aluminium-containing ZSM-5 can be obtained also in the absence of an organic template ( LJJK but the synthesis of silicate I seems to require the presence of an organic molecule in the reaction mixture ( 3K... 

Significant Parameters in the Synthesis of Large Alkaline-Free MFI-Type Zeolites and AFI-Type Aluminophosphates... 

With regard to MFI-type zeolites, statistic factorial design proved to be extremely helpful. For alkaline-free systems, factors... 

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