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The identification of the NaY zeolite was carried out through XRD analysis. It was compared with the identification peaks of a commercially available NaY zeolite (CBV-100, SiO2/Al2O35.1) provided by Zeolyst International USA. Figures 3.2 and

3.3 show that the major peaks of identification are located at 2 23.6,26.9,and31.3.

The pore volume of starting silica gel was very important as it provided the information about how much volume of aluminum nitrate nonahydrate was needed to be gradually added. Also the average pore diameter of the silica particle provided the information about how much the pores narrowed with the gradual addition of aluminum nitrate nonahydrate. The BET surface area of the starting silica gel was found to be 257 m2 /g . The BJH adsorption pore volume and average pore diameter were found to

be 1.56 cm3/g and 248



A , respectively. The pore volume and the average pore Figure 3.2: X-ray diffraction pattern of NaY zeolite synthesized in pre-shaped silica particles

diameter of the silica particles gradually started to decrease with the addition of alumina.

The average pore diameter was reduced to 146



A by the third stage of alumina addition.

After the synthesis reaction, the BET surface area of the product was found to be 412

g

m2 / , and the BJH adsorption pore volume and average pore diameter were found to

be 0.024 cm3/g and 138



A. The change in the surface area is due to the growth of NaY zeolite in the pores of silica gel. However, the decrease in the pore volume and the average pore size is attributed to the space occupation by the growing zeolite crystals within the pore of silica particles. It seems that zeolite particles have grown on and within the walls of the pores and have blocked the pores to some extent. This may be explained in a way that initially, we had an empty glass of water and later it was filled with the crystals of zeolites, thus reducing the volume of the glass. However, the diameter of the glass is not much affected. The small drop in the average pore diameter of the pores before and after the addition of NaOH, and the synthesis reaction further support our hypothesis.

The SiO2 /Al2O3 ratio was determined analytically using XRF and EDX

methods. It was also determined stoichiometrically while increasing the alumina in silica in several stages. The final stoichiometrical ratio was calculated to be 6.09, while the analytical ratios through XRF and average EDX were found to be 6 and 6.3, respectively. This shows that the bulk ratio determined through XRF and ratios in the crystals determined by EDX were very close to each other. The XRF results covered the bulk of the material and were able to acquire the composition of several layers of the material. Whereas the EDX analysis was more localized and covered a depth of only few layers of the material. The overall observation through both analytical techniques strengthened the concept that in solid-solid transformation the SiO₂ /Al₂O₃ ratios of the crystals are not much different from the bulk reagents ratio (Derouane et al. 1981).

SEM imaging was carried out for the product in order to visualize the morphology of the NaY zeolite, the crystal size and its distribution. Figures 3.4 and 3.5 represent the SEM images of NaY zeolite and its zoomed view. Since the crystals were imbedded inside the silica particles, the silica particles were cracked opened for visual analysis through SEM equipment. It can be seen that the clusters of zeolites in the range of 1-2 micrometer were formed instead of separated singles crystals which was due to solid- solid transformation (Derouane et al. 1981). The size of the crystallites in clusters was in the range of 100-200nm, which exhibited a narrower crystal size distribution. It can also be observed in Figure 3.4 that the crystals were uniformly distributed throughout the silica particles. The growth of crystals on the outer surface of silica particles was not observed, which indicated that the chemicals were uniformly penetrated in the particles and that the alumina was deposited inside the mesopores of silica particles and not accumulated on the surface of the particles.

Figure 3.4: SEM image of laboratory synthesized NaY zeolite. The cracked open view of the silica particle (50m) shows the intact outer crust of the particle with embedded clusters of NaY zeolite (12m).

Figure 3.5: Zoomed view of NaY zeolite crystals (100200nm) in a cluster within the silica particle.

This observation also strengthened the idea that the remaining outer layer of the silica particle may keep the crystals encapsulated and can be used directly for FCC application after a suitable ion-exchange of NaY zeolite. In this scenario, any further reduction in crystal size may add to its activity, and the nanosized crystals embedded in silica particles may be used for any appropriate application.

3.5CONCLUSIONS

It can be concluded that a better technique is emerging by using a dry process, which may lead to maximum production of NaY zeolite with reduction in process time. Also, a narrower particle size distribution is achievable with a better control on the crystal size due to their growth in confined space. Due to the size of crystals in the nanometer range, a reduction in diffusion resistance is expected. A saving on consumption of chemicals was obtained in the sense that a negligible chemical waste was generated. Also, using only NaOH solution for the synthesis of NaY zeolite eliminated the use of an organic or inorganic structure directing agent. This also saved on expensive chemicals. Since the nanosized crystals were formed within the silica particles, therefore, their handling would be very easy and may readily be used for any suitable application.

3.6REFERENCES

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Schmidt, I., Madsen, C., Jacobsen, C. J. H. "Confined space synthesis. A Novel Route to Nanosized Zeolites." Inorg.Chem., 2000, 39 (11), 2279-2283.

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CHAPTER 4: EFFECTS OF VARIOUS OPERATING CONDITIONS ON THE