Catalysis Today, Vol.243, 141-152, 2015
Remarkable catalytic properties of hierarchical zeolite-Beta in epoxide rearrangement reactions
Hierarchical Beta zeolites with enhanced accessibility obtained by crystallization of silanized zeolitic seeds were synthesized and investigated as catalysts for epoxide rearrangement reactions. On the other hand, hybrid zeolitic-mesoporous materials prepared from Beta protozeolitic units, and later assembled around cetyltrimethyl ammonium bromide (CTAB), were also synthesized for comparison purposes. Textural and structural properties were studied by N-2 and Ar adsorption isotherms, X-ray diffraction (XRD) and transmission electron microscopy (TEM). The coordination and stability of the Al atoms were investigated by Al-27 MAS NMR. The acidic properties were analyzed by NH3 temperature programme desorption (TPD), and by FUR probe pyridine adsorption-desorption to get insights on their acidic features and population of Bronsted and Lewis acidity. These zeolitic type materials featured additional porosity and enhanced textural properties compared with the conventional Beta zeolite and Al-MCM-41. Likewise, their acidic properties were modified, the distribution and strength of Bronsted and Lewis acid sites being different compared to the reference samples. These materials were tested in the liquid phase rearrangement of cyclic, branched, and linear epoxides with different sizes to explore how the acidity and the improved diffusion of the substrates through the channels influence their catalytic behaviour. In overall, hierarchical Beta zeolite exhibits the best combination of catalytic activity and selectivity due to enhanced accessibility and appropriate balance of Bronsted and Lewis acid sites. These results confirm that the hierarchical Beta zeolite is a potentially interesting catalyst for epoxide rearrangement reactions. (C) 2014 Elsevier B.V. All rights reserved.
Keywords:Hierarchical zeolites;Zeolite Beta;Hybrid zeolitic-mesostructured materials;Epoxide rearrangement