MCM-41 explained

MCM-41 (Mobil Composition of Matter No. 41) is a mesoporous material with a hierarchical structure from a family of silicate and alumosilicate solids that were first developed by researchers at Mobil Oil Corporation[1] and that can be used as catalysts or catalyst supports.[2]

Structure

MCM-41 consists of a regular arrangement of cylindrical mesopores that form a one-dimensional pore system. It is characterized by an independently adjustable pore diameter, a sharp pore distribution, a large surface and a large pore volume. The pores are larger than with zeolites and the pore distribution can easily be adjusted.[3] The mesopores have a diameter of 2 nm to 6.5 nm.

Properties

Contrary to zeolites, the framework of MCM-41 has no bronsted acid centers because there is no aluminium contained in the lattice. The acidity of alumina-doped MCM-41 therefore is comparable to that of the amorphous alumosilicates.

MCM-41 is not hydrothermally stable because of the slight wall thickness and the low degree of cross-linking of the silicate units.

Synthesis

To achieve a defined pore diameter surfactants are used that form micelles in the synthesis solution. These micelles form templates that help build up the mesoporous framework. For MCM-41 mostly cetyltrimethylammonium bromide (CTAB) is used.

The surfactant first forms rod-like micelles that subsequently align into hexagonal arrays. After adding silica species these cover the rods. Later, calcination leads to a condensation of the silanol groups so that the silicon atoms are bridged by oxygen atoms. The organic template is oxidized and disappears.

Uses

MCM-41, as the zeolites, are widely used as catalytic cracking.[4] MCM-41 type materials have been widely used as support of heterogeneous catalysts [5] and also used for separations.

Notes and References

  1. Kresge . C. T. . Leonowicz . M. E. . Roth . W. J. . Vartuli . J. C. . Beck . J. S. . 1992 . Ordered mesoporous molecular sieves synthesized by a liquid-crystal template mechanism . Nature . en . 359 . 6397 . 710–712 . 10.1038/359710a0 . 4249872 . 0028-0836.
  2. http://www-brs.ub.ruhr-uni-bochum.de/netahtml/HSS/Diss/ReichingerMarkus/diss.pdf Reichinger, M. (2007) Poröse Silikate mit hierarchischer Porenstruktur: Synthese von mikro-/mesoporösem MCM-41 und MCM-48 Materialien aus zeolithischen Baueinheiten des MFI-Gerüststrukturtyps
  3. Silaghi, M.-C., Chizallet, C., Raybaud, P.. Challenges on molecular aspects of dealumination and desilication of zeolites. Microporous and Mesoporous Materials. 191. 82–96. 10.1016/j.micromeso.2014.02.040. 2014.
  4. Catalysis by Crystalline Mesoporous Molecular Sieves. Sayari, Abdelhamid. Chemistry of Materials. 1996. 8. 8 . 1840–1852. 10.1021/cm950585+.
  5. P. Chatterjee . H. Wang . J. S. Manzano . U. Kanbur. A. D. Sadow. I. I. Slowing. Surface ligands enhance the catalytic activity of supported Au nanoparticles for the aerobic α-oxidation of amines to amides. Catal. Sci. Technol.. 12. 6. 1922–1933. 2022. 10.1039/D1CY02121D. 246575960 . free.