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. 2022 Dec 15;27(24):8934.
doi: 10.3390/molecules27248934.

Can We Form Mesoporous Zeolites by Steam Assisted Crystallization of MCM-41?

Iane M S Souza  1   2 , Sibele B C Pergher  2 , Alexander Sachse  1
Affiliations

Can We Form Mesoporous Zeolites by Steam Assisted Crystallization of MCM-41?

Iane M S Souza et al. Molecules. .

Abstract

The possibility of crystallizing silicalite-1 (MFI) from the pore walls of as-synthesized MCM-41 via steam-assisted crystallization (SAC) was thoroughly investigated. A kinetic study was conducted through the impregnation of as-synthesized MCM-41 with the structure-directing agent tetrapropyl-ammonium hydroxide (TPAOH). Materials obtained after different SAC treatment times (1−288 h) were characterized by XRD, nitrogen physisorption at 77 K, TGA/DTA, and SEM. The achieved results allowed us to conclude that during SAC treatment, rapid destruction of the hexagonal mesophase occurs with the enlargement of mesopores, probably by their coalescence, until achieving non-porous amorphous silica. Only thereafter is the crystallization of the MFI phase evidenced through the development of micron-sized (>10 µm) MFI structured crystals. This study suggests the probable practical impossibility of even partial crystallization of the pore walls of mesoporous materials by SAC.

Keywords: MCM-41; MFI; hierarchical zeolites; silicalite-1; steam assisted crystallization.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
X-ray diffraction patterns for the as-synthetized MCM-41 (AS-MCM-41) and the calcined MCM-41 (MCM-41).
Figure 2
Figure 2
Low angle (a) and wide angle (b) X-ray diffraction patterns of materials after indicated times of SAC treatment and the evolution of zeolite crystallinity as a function of the SAC treatment time (c).
Figure 3
Figure 3
Nitrogen physisorption isotherms at 77 K (a) and DFT pore size distribution (b) for calcined materials achieved after different times of SAC treatment.
Figure 4
Figure 4
Differential thermogravimetric analysis (DTA) (a) and weight loss (b) for materials after indicated SAC times. The blue and black symbols represent the cumulative weight loss between 120 and 350 °C (W1) and 350 and 900 °C (W2).
Figure 5
Figure 5
SEM images of parent MCM-41 ((a), length of the scale bars of 1 µm) and for materials achieved after SAC treatment for 8 h ((b), length of the scale bars of 1 µm), 24 h ((c), length of the scale bars of 10 µm), 96 h ((d), length of the scale bars of 1 µm), and 288 h ((e), length of the scale bars of 10 µm).
See this image and copyright information in PMC

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