MCM-41
{{Short description|Catalyst or catalyst support material}}
File:Mesoporous carbon TEM.jpg
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{{Cite journal |last1=Kresge |first1=C. T. |last2=Leonowicz |first2=M. E. |last3=Roth |first3=W. J. |last4=Vartuli |first4=J. C. |last5=Beck |first5=J. S. |date=1992 |title=Ordered mesoporous molecular sieves synthesized by a liquid-crystal template mechanism |url=http://www.nature.com/articles/359710a0 |journal=Nature |language=en |volume=359 |issue=6397 |pages=710–712 |doi=10.1038/359710a0 |s2cid=4249872 |issn=0028-0836|url-access=subscription }} and that can be used as catalysts or catalyst supports.[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], Dissertation Ruhr-Universität Bochum (in German)
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.{{cite journal|author=Silaghi, M.-C., Chizallet, C., Raybaud, P.|title=Challenges on molecular aspects of dealumination and desilication of zeolites|journal=Microporous and Mesoporous Materials|volume=191|pages=82–96|doi=10.1016/j.micromeso.2014.02.040|year=2014}} 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.{{cite journal|title=Catalysis by Crystalline Mesoporous Molecular Sieves|author=Sayari, Abdelhamid|journal= Chemistry of Materials|year=1996|volume=8|issue=8 |pages=1840–1852|doi=10.1021/cm950585+}} MCM-41 type materials have been widely used as support of heterogeneous catalysts {{cite journal|author1=P. Chatterjee |author2=H. Wang |author3=J. S. Manzano |author4=U. Kanbur|author5=A. D. Sadow|author6=I. I. Slowing|title=Surface ligands enhance the catalytic activity of supported Au nanoparticles for the aerobic α-oxidation of amines to amides|journal= Catal. Sci. Technol.|volume=12|issue=6|pages=1922–1933|year=2022|doi=10.1039/D1CY02121D|s2cid=246575960 |doi-access=free}} and also used for separations.