Hierarchical Beta zeolites obtained in concentrated reaction mixtures as catalysts in tetrahydropyranylation of alcohols
Abstract
Hierarchical zeolites consisting of Beta nanoparticles (15-40 nm) were obtained via hydrothermal treatment of a concentrated zeolite gel-precursor (H2O/Si = 2.5-14) without utilization of complex SDAs. The proposed approach is based on the formation of a large number of zeolite nuclei under particular crystallization conditions, followed by their agglomeration resulting in the dense packing of the particles preventing their further growth.
The micelles of cetyltrimethylammonium bromide (CTAB) can be used to additionally limit the growth of zeolite nanoparticles during hydrothermal treatment of concentrated reaction mixtures. Such deceleration of crystallization promotes the formation of highly porous X-ray amorphous nanosized aluminosilicate.
Due to the developed mesoporosity and increased accessibility to the acid sites for the molecules of a large size, hierarchical Beta zeolites obtained in the presence of CTAB demonstrate high catalytic activity in the reaction of bulky alcohols (1-octadecanol and 1-adamantanemethanol) with 3,4-dihydro-2H-pyran.