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

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.