Partial Transformation of MCM-41 Material into Zeolites:  Formation of Nanosized MFI Type Crystallites

Abstract

A new potentially catalytic material has been developed by partial recrystallization of the porewall of MCM-41. Recrystallization is induced by impregnation of MCM-41 with tetrapropylammonium hydroxide followed by a hydrothermal treatment. This procedure resulted in the formation of small particles of approximately 3 nm, which can be observed with TEM. The fact that the formation of these particles resembles the first stages of ZSM-5 formation and the fact that a templating material is used, which is also frequently applied in the synthesis of ZSM-5, suggest that the 3 nm particles have a ZSM-5 structure. Furthermore, 13 C NMR on recrystallized MCM-41 shows a split-up of the methyl signal of TPA, which is also known to be present in as-synthesized ZSM-5. After calcination of the recrystallized material the small crystallites could no longer be observed, although IR measurements show still some ZSM-5-like acidity to be present. Other, milder calcination routes should be developed in order to preserve the ZSM-5 crystallites. Another stability problem encountered concerns the stability of the MCM-41 since the hydrothermal treatment severely damaged the framework. It was found that the use of a template molecule, hexadecylamine, to support the framework during the recrystallization was beneficial.

MFI Zeolite with Small and Uniform Intracrystal Mesopores

“…Recently, several efforts have been made to reduce the diffusion path length in zeolites by confining crystal growth to a nanometer length scale [2][3][4][5][6][7][8] or by providing intracrystal mesopores during synthesis.[9-13] The latter strategy is intrinsically appealing, in part, because it precludes the need for colloidal crystal formation and avoids the drawbacks associated with nanoparticle processing. Moreover, the presence of mesopores in zeolite crystals offers the possibility of improving product selectivity in the catalytic cracking of polymeric molecules.…”

Zeolite Nanocrystals Inside Mesoporous TUD‐1: A High‐Performance Catalytic Composite

“…However, these small clusters or nuclei easily loose their integrity during activation through calcination at high temperatures. [16] An issue that is also of potential concern when using zeolite seeds, as reported by Prokesova, et al [18] Moreover, the physicochemical properties of both the zeolite and the mesoporous materials are difficult to tune independently as the zeolite synthesis is coupled with the mesopore formation.…”

Micro/Mesoporous Zeolitic Composites: Recent Developments in Synthesis and Catalytic Applications

“…The resulting materials, coded as PNA-1 and PNA-2 corresponding to the parent MCM-41 and HMS respectively, exhibit disordered mesoporous materials with embryonal ZSM-5 in the mesoporous walls. Later, Verhoef et al [74] demonstrated the formation of small particles containing ZSM-5 structure of approximately 3 nm during the partial transformation of mesoporous walls of MCM-41 under hydrothermal treatment. Attempts to create well-defined ZSM-5 nanocrystals by partial recrystallization of MCM-41 type materials often lead to the collapse of the MCM-41 framework and the formation of segregated zeolite crystals [75,76].…”