Y, zeolite

Dihydropyran, H-Y Zeolite, hexane, reflux, 60-95% yield. H-Rho Zeolite can also be used as a catalyst. "... 

For primary aromatic amines dimethyl carbonate, Y-Zeolite, 130-150°, 72-93% yields. ... 

Bronsted acid sites in HY-zeolites mainly originate from protons that neutralize the alumina tetrahedra. When HY-zeolite (X- and Y-zeolites... 

The elementary building block of the zeolite crystal is a unit cell. The unit cell size (UCS) is the distance between the repeating cells in the zeolite structure. One unit cell in a typical fresh Y-zeolite lathee contains 192 framework atomic positions 55 atoms of aluminum and 1atoms of silicon. This corresponds to a silica (SiOj) to alumina (AI.O,) molal ratio (SAR) of 5. The UCS is an important parameter in characterizing the zeolite structure. 

The zeolites with applications to FCC are Type X, Type Y, and ZSM-5. Both X and Y zeolites have essentially the same crystalline structure. The X zeolite has a lower silica-alumina ratio than the Y zeolite. The X zeolite also has a lower thermal and hydrothermal... 

NaY zeolite is produced by digesting a mixture of silica, alumina, and caustic for several hours at a prescribed temperature until crystallization occurs (Figure 3-8). Typical sources of silica and alumina are sodium silicate and sodium aluminate. Crystallization of Y-zeolite typically takes 10 hours at about 210°F (100°C). Production of a quality zeolite requires proper control of temperature, time, and pH of the crystallization solution. NaY zeolite is separated after filtering and water-washing of the crystalline solution. 

ZSM-5 is Mobil Oil s proprietary shape-selective zeolite that has a different pore structure from that of Y-zeolite. The pore size of ZSM-5 is smaller than that of Y-zeolite (5.1°A to 5.6°A versus 8°A to 9 A). In addition, the pore arrangement of ZSM-5 is different from Y-zeolite, as shown in Figure 3-16. The shape selectivity of ZSM-5 allows... 

The breakthrough in FCC catalyst was the use of X and Y zeolites during the early 1960s. The addition of these zeolites substantially increased catalyst activity and selectivity. Product distribution with a zeolite-containing catalyst is different from the distribution with an amorphous silica-alumina catalyst (Table 4-3). In addition, zeolites are 1,000 times more active than the amorphous silica alumina catalysts. 

The cations that replace the sodium ions determine the catalyst s activity and selectivity. Zeolites are synthesized in an alkaline environment such as sodium hydroxide, producing a soda-Y zeolite. These soda-Y zeolites have little stability but the sodium can be easily... 

Soda Y Zeolite is a crystallized form of Y-faujasite before any ion exchanges occur. 

Good yields and high diastereoselectivities were obtained by using zeolites in combination with Lewis-acid catalyst [21]. Table 4.7 illustrates some examples of Diels-Alder reactions of cyclopentadiene, cyclohexadiene and furan with methyl acrylate. Na-Y and Ce-Y zeolites gave excellent results for the cycloadditions of carbocyclic dienes, and combining these zeolites with anhydrous ZnBr2 further enhanced the endo diastereoselectivity of the reaction. An exception is the cycloaddition of furan that occurred considerably faster and with better yield, in comparison with the classic procedure [22], when performed in the presence of sole zeolites. 

In an early paper by our group (ref. 19) halobenzenes are brominated at 298 K in the liquid phase over various Y-zeolites (Fig. 7). Improved p/o-ratios with respect to conventional (FeBr3) catalysis are observed. 

The order in reactivity in the Y-zeolite catalyzed bromination found is toluene > benzene > fluorobenzene > chlorobenzene > bromobenzene... 

These N,N-chelating hgands were then covalently grafted on a modified Y-zeolite containing supermicropores . The selectivities observed were low (up to 11% ee) but led to similar values when comparing the imsupported and zeolite-supported Cu complexes. Interestingly, however, the zeolite catalysts could be recovered and reused several times with no loss of activity. 

Method B was also used in the preparation of occluded (salen)Cr complexes. ligands Ih and li were prepared within the pores of Cr -exchanged EMT and Y zeolites, respectively [25]. These complexes were tested as catalysts in the ring opening of meso-epoxides with trimethylsilyl azide (Scheme 4). The occluded complexes showed a dramatic decrease in catalytic... 

Table 12 Results of reactions of ethyl glyoxylate with different alkenes, catalyzed by several bis(oxazoline)-copper complexes immobilized on Y zeolite...

Figure 2.3 3D-TEM reconstruction of (a) severely steamed and subsequently acid-leached Y zeolite [22] and (b) desilicated ZSM-5 zeolite crystal [24]. The mesopores in the crystal are shown as lighter gray tones.

Fig. 1. a) Standard protonation enthalpy in secondary carbenium ion formation on H-(US)Y-zeolites with a varying Si/Al ratio, b) Effect of the average acid strength for a series of H-(US)Y zeolites experimental (symbols) versus calculated results based on the parameter values obtained in [11] (lines) for n-nonane conversion as a function of the space time at 506 K, 0.45 MPa, Hj/HC = 13.13 (Si/Al-ratios 2.6, 18, 60)... 

Y zeolite from kaolin taken in Yen Bai-Vietnam synthesis, characterization and catalytic activity for the cracking of n-heptane... 

This paper is concerned with the synthesis of Y zeolite with Si02/Al203 ratio of 4.5 from kaolin taken in Yen Bai-Vietnam and their catal3dic activity for the cracking of n-heptane. The synthesized sample (NaYl) showed the Y zeolite crystallinity of 53% and PI zeolite crystallinity of 32%, and exhibited good thermal stability up to 880 C. The activity and the stability of HYl turned out to be lower than those of standard sample (HYs), but the toluene selectivity was higher. The conversion of n-heptane to toluene might be due to the metal oxide impurities, which was present in the raw materials and this indicates the potential application of this zeolite for the conversion of n-parafRn to aromatics. 

Y zeolites synthesized from pure chemicals have now been used as the main composition of FCC catalysts [1-4]. However, the application of Y zeolites synthesized from kaolin in the catalytic processes is still limited. The refinery and petrochemical industry is being built in Vietnam, so the synthesis of Y zeolites from domestic materials and minerals is necessary [4]. In this paper, the initial results in the synfliesis of Y zeolites with Si02/Al203 ratio of 4.5 fiom kaolin taken in Yen Bai-Vietnam and their catalytic activity for the cracking of n-heptane are reported. 

Fig. 3 shows that NaYl contains two types of crystals Y zeolite in cubic form and Pj zeolite in spherical form with diameter of about 5 pm and 3 pm, respectively. On the other hand, NaYs contains only crystals of Y zeolite in spherical form with diameter of about 0.5 pm. It is clearly demonstrated that the diameter of zeolite synthesized fi om kaolin is much larger than that of zeolite synthesized from pine chemiceils. 

Sample CEC, meq Ba /100g ACsHs % Y zeolite PI zeolite Thermal crystallinity crystallinity stability, °C Si02/Al203 FS203 ratio wt.% FeO wt. % TiOj wt.%... 

Catalytic cracking with faujasite zeolites X and y zeolites... 

Isomerization of a-pinene epoxide to campholenic aldehyde, an intermediate for perfumery chemicals, has been carried out elegantly with ultra stable Y-zeolite. 

Large-pore zeolites such as Y zeolites are efficient for the hydroamination of several olefins. For example, propene reacts with NH3 over SK-500 (a pelleted lanthanum-exchanged zeolite) or La-Y or H-Y zeolites with 6-15% conversion to give i-PrNHj with high selectivity (95-100%) (Eq. 4.5) [50]. 

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