FAU type zeolites

FAU-type Zeolites X and Y. Several equations have been proposed for this purpose [49], The number of aluminum atoms per unit cell in the FAU-type structure, XA1, can thus be calculated according to... 

Most importantly, biomass pyrolysis will be carried out at remote locations, and in distributed manner. Thus, the catalysts should be cheap and simple to use. Acidic clays, silica aluminas and H-FAU type zeolites are relatively cheap and robust materials, can be mixed easily with heat carriers, and used for pyrolysis. Efficient contact between the solids (catalyst and biomass) to maximize catalytic action is one of the challenges that need to be overcome. 

FAU type zeolites exchanged with many different cations (Na, K, Ba, Cu, Ni, Li, Rb, Sr, Cs, etc.) have been extensively studied. The unit cell contents of hydrated FAU type zeolite can be represented as M,j(H20)y [A Sii92 0384] -FAU, where x is the number of A1 atoms per unit cell and M is a monovalent cation (or one-half of a divalent cation, etc.). The number of A1 atoms per cell can vary from 96 to less than 4 (Si/Al ratios of 1 to more than 50). Zeolite X refers to zeolites with between 96 and 77 A1 atoms per cell (Si/Al ratios between 1 and 1.5) and Zeolite Y refers to zeolites with less than 76 A1 atoms per cell (Si/Al ratios higher than 1.5). 

Figure 4.28 Effect of steaming and calcination on Bronsted and Lewis acid site strength distributions of a FAU-type zeolite as determined by pyridine adsorption/desorption IR.

The selectivity of n-hexane hydrocarver-sion on MOR-, MAZ-, and FAU-type zeolites. . Catal, 228,121-129. 

Fig. 22. (a) Connection mode in FAU type zeolite, showing the supercages (Z9) (b) connection mode in EMT type zeolite, showing the hypocages (79). 

Positively charged stopcocks can be plugged in the zeolite channels by ion exchange, whereas neutral stopcocks can be added by dehydration of the zeolite channels and adsorption from a nonaqueous solution or from the gas phase. The zeolite s external surface consists of a coat and a base. These two surfaces differ in a number of properties so that the interactions can be tuned. For MFI- and FAU-type zeolites, as an example, it was reported that guest molecules bind to the holes on the external surface much more strongly than on the framework between the holes [38,39]. 

Scheme 10.3 Formation of MePc complexes in the supercages of FAU-type zeolites via tetramerization of 1,2-dicyanobenzene around transition metal exchanged zeolite.

At present, among HMS two main zeolitic types, available at a commercial scale, are receiving attention. The first one belongs to the MFI type and can be obtained directly by synthesis. The second is prepared by dealumination of FAU type zeolite in order to increase the Si/Al ratio above ca. 50. 

Noble metals are preferred when non chlorinated VOCs have to be destroyed. For reasons of accessibility, FAU type zeolites are the most frequently employed catalysts and a parameter of utmost importance is the number of accessible metal sites and the reductibility. This was recently put in evidence for the o-xylene oxidation on Pd-FAU catalysts (19). Pd° was proposed as an active site, and the specific activity increased with the ratio (nPd)/nacid. A lower acidity (high Si/Al ratio) favors the Pd2 and PdO reductibility, and decreases the extent of coke formation. 

Jeong BH, Sotowa KI, and Kusakabe K. Catalytic dehydrogenation of cyclohexane in an FAU-type zeolite membrane reactor. J Membr 5d2003 224 151-158. 

Vibrational spectra Develop a force field to explicitly distinguish between Al and Si in FAU-type zeolites 79 ... 

Cerium-, copper-cerium coexchanged ZSM-5, copper-MCM-22, copper- and cerium-EMT type zeolite, copper-FAU type zeolite and copper-Beta exhibit an activity of the same order as that of copper-ZSM-5 in NOx reduction under simulated Diesel exhaust conditions. Propene was used as the reducing agent. The catalysts were used in a powder form and their activities tested in a fixed-bed flow reactor at a space velocity of 50 000 H . Copper-SAPO-34 and cerium- and gallium-EMT type zeolite have a moderate activity under the same conditions. The presence of water vapor inhibits the activity of EMT-zeolites. When an ageing procedure is carried out on copper-EMT type zeolite, dealumination occurs. The increase of the Si/Al ratio of the zeolite does not limit the dealumination process. The exchange of the zeolite with lanthanum prevents the zeolite from dealumination but leads to a loss of the catalytic activity. 

Many catalysts exhibit a catalytic activity for NO reduction, under conditions of Diesel exhausts, not very inferior to that of ZSM-5, especially copper-MCM-22, copper-EMT, copper FAU-type zeolites and copper-Beta. EMT-catalysts which present a good potential for Diesel exhaust after-treatment suffer from deactivation in the presence of water as it is the case for ZSM-5 catalysts. Dealumination was a significant cause of this loss of activity when the catalysts were aged. It was not possible to avoid dealumination while keeping the catalyst... 

Investigations of the hydrothermal stability of catalysts such as copper-MCM-22, copper FAU-type zeolites and copper-Beta zeolite should be carried out. 

Among the many possible candidates for catalyst support, some zeolite topologies constitute a particular group of carriers. It seems that Romanovski et al. [4] were the very first to report an in situ synthesis of transition metal Pc (MePc) complexes in the supercages of faujasite type zeolites. The synthesis was later successfully repeated by Schulz-Ekloff et al. [5] and Herron [6]. It is assumed that formation of MePc out of four 1,2-dicyanobenzene (DCB) molecules in the supercages of Me-exchanged faujasite (FAU)-type zeolites is accompanied by a two-electron oxidation of (residual) water molecules ... 

Por the hydrated state, we can reasonably expect that the site I and site II cations are completely solvated with (three) water molecules. The interaction enerqy w can therefore he incorporated into e-p ejj and ejjj, such that the above equations formally reduce to those of the dehydrated state. Van Dun et. al. (2) found that as a function of the Al content, the cation distributions in dehydrated Na-exchanged FAU-type zeolites could he accurately predicted if it was assumed that the enerqy level differences relative to site I varied linearly with the framework negative charae. At around 48 Al/unit cell, the site preference chanqes from II > I > I (low Al content) to I > II > I (high Al content). 

This material was obtained by direct synthesis using a modified orqanic template procedure previously reported (3). Its Al content, and of all others, was determined from the variation of the unit cell constant with Al content for a range of fully K-exchanged hydrated zeolites (5 ). The Al content is then calculated as (a0 - 25.127)/0.011388, which applies only to h-K-FAU-type zeolites. 2<,Si nmr and chemical analyses confirmed these data. 

P-13 - Permanent storage of chromium in hardened FAU-type zeolite /cement pastes... 

FTIR spectroscopy was employed by Brock et al. [933] to follow in situ the decomposition of sodium azide on FAU-type zeolites with different nsi/nAj ratios. The main bands in the complex spectra occurred at 2072-2079 (Na-X) and at 2066-2079 cm (Na-Y), depending on the nsi/n i ratio, and declined on progressive decomposition at increasing temperatures, which caused other bands intermediately to appear. 

Comparing the exchange rates per acid site for FAU and MFI (Fig. Schoofs found that for the same Al/Si + A1 ratio, the exchange rate was higher for MFI than for FAU-type zeolites in accordance with an important structural influence. A kinetic isotope effect (kn/kD = 1.7) was measured for MFI type zeolite, suggesting a faster exchange between CD4 and... 

H2O, CO2 and N2 removed from air by non-cryogenic pressure swing adsorption over LiX zeolite, leaving > 95% O2 High silica zeolites adsorb unburnt hydrocarbons and desorb them as the engine and the catalytic converter warm up Shape selective Ca-A zeolite (5A) adsorbs linear but not branched hydrocarbons Shape selective MFI type zeolites (silicalite) adsorb para- but not ortho- or meta-xylenes. FAU type zeolites are also effective for this separation under simulated moving bed conditions... 

Sato K, Sugimoto K, Sekine Y, Takada M, Matsukata M, Nakane T. Application of FAU-type zeolite membranes to vapor/gas separation under high pressure and high temperature up to 5 MPa and 180°C. Micropor Mesopor Mater 2007 101 312-318. 

Zhu G, Li Y, Chen H, Liu J, Yang W. An In situ approach to synthesize pure phase FAU-type zeolite membranes Effect of ageing and formation mechanism. J Mater Sci 2008 43 3729-3288. 

Figure 17.7 Gas permeance and CO2/N2 separation factor as a function of the temperature for equimolar CO2-N2 mixture in dry and moist conditions. Reprinted from X. Gu, J. Dong and T. M. Nenoff, Synthesis of defect free FAU-type zeolite membranes and separation for dry and moist CO2/ N2 mixtures, Industrial and Engineering Chemistry Research, 44, 937-944, 2005, with permission from ACS.

Jeong, Sotowa, and Kusakabe (2004) simulated the catalytic dehydrogenation of cyclohexane in an FAU-type zeolite membrane reactor. The cyclohexane conversion enhanced in the zeohte membrane reactor, which was more dependent on the permeance than the separation factor. Table 21.3 presents a summary of some of the membrane reactors used for cyclohexane dehydrogenation. 

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