Hybrid crystalline/non-crystalline aluminosilicates having a combined micro- and mesoporous structure have attracted a great deal of attention because their potential applications in catalysis and adsorption technologies. The high surface acidity arising from the zeolitic component together with the wide pore system of the MCM-41 mesoporous phase, makes it interesting enough for potential catalytic applications, provided that further hydrothermal stability is accomplished .
The microporous molecular sieves having high surface acidity and pore diameters of less than 1 nm, are currently employed in the refining industry as the active phases of FCC catalysts . However, the progressive complexity of the heavy crude fractions motivates the search of new large-pore materials, for adsorbing bulky molecules and promoting their catalytic conversion . In this way, the physical interaction or even the possible inclusion of zeolitic crystallites (i. e. ZSM-5, betha4) into the MCM-415 structure could increase the active surface sites available in this system, which could open a range of potential applications in FCC, isomerization and hydrocracking processes.
In this viewpoint, this work presents the synthesis at low temperature (363-373K) and characterization of hybrid Zeolites/MCM-41 materials. XRD, TEM, TGA and N2 adsorption (BET) methods were used to characterize their main structural and textural features, respectively.
Results and Discussion
The XRD patterns of the separate phases MCM-41 and ZSM-5, respectively were used as reference. Also, a physical mixture of MCM-41 and ZSM-5 was made to control the possible growth of crystallites in the synthesis batch. The XRD pattern of this mixture does not observe the typical peaks of the zeolitic phase, as observed in on the reference, because the overall amount of ZSM5 is not enough to overcome the XRD background or the crystallite size is too small. The XRD pattern of the hybrid MZSM-1 material can be compared with the patterns shown of MCM-41 and ZSM-5, where one observes a similar set of diffraction peaks i.e. interplanar spacing d (Å) = 11.1, 10.0, 7.4, 7.1, 6.3, 5.9, 5.56, 5.01, 4.6, 4.2,3.8, 3.7, 3.0, 2.94 and 2.99, which correspond to the ZSM-5 phase. Peaks having values of 39.8, 22.9, 19.8 and 14.9 Å correspond to MCM-41. Therefore, the hybrid MZSM-1 materials seem to have both micro- and mesoporous characteristics.
The pore diameter distribution of these solids indicates the formation of pores of about 26 Å. In addition, transmission electron microscopy images of the hybrid materials, show a well-defined order of the pore structure and their hexagonal symmetry.
It was demonstrated that zeolitic phases grow in the synthesis batch of non-crystalline mesoporous sieves, according to XRD results. These hybrid materials display both crystalline (ZSM5) and non-crystalline (MCM-41) phases, which means probably that ZSM-5 crystallites are outside of the MCM-41 structure.
1. Lui, Y.; Pinnavaia, T.J. Chem. Matter. 14 (2002) 3.
2. Guidry, H. U. S. Patent 4,144,194. March, (1979)
3. Corma A., Grande M. S. Journal of catalysis, 159 (1996) 375-382.
4. Argauer, R.; Kensington, M.; Landolt, G.; USA Patent 3,702,886, Nov. (1972)
5. Kresge, C.; Leonowicz, M.; Roth, W.; Vartulli, J.; Beck, J.; Nature 359 (1992) 710
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