Applications of M41S and related materials

Most potential applications reported in the literature use MCM-41, HMS or FSM-16 type of materials. Patents dealing not only with the applications, but also with the synthesis of crystalline mesoporous materials are almost exclusively assigned to Mobil Oil Corporation. Extensive lists of these patents are provided as appendixes. Catalytic applications may be conveniently divided into three categories (i) acid catalysis, (ii) liquid phase redox catalysis, and (iii) other applications. 

Acid sites in mesoporous silicates can be generated either by isomorphous substitution of trivalent cations such as A1 or B for Si, or by adding an acidic component such as a heteropolyacid, an ultra stable Y (USY) or a A1 containing ZSM-5 zeolite. 

Shinoda et al. [229] found that FSM-16 mesoporous aluminosilicate compares favorably with the currently used liquid acid BFj.OEtj for the synthesis of wreso-tetraarylporphyrins from the corresponding aromatic aldehydes and pyrrole. In addition, contrary to soluble catalysts and to KIO acid treated montmonrillonite, FSM-16 could be used repeatedly after regeneration by calcination at 500 °C. 

Since the discovery in the early 80 s of the remarkable catalytic activity of Ti-modified silicalite-1 (TS-1) in the selective oxidation of organic substrates by dilute H2O2, the field of transition metal modified zeolites grew tremendously as shown in a number of recent reviews [156,235,236]. In addition to its hydrophobicity, the major role of the zeolite matrix is the stabilization of isolated redox centers. However, the limited accessibility of these sites precluded the use of large substrate molecules. The discovery of crystalline mesoporous silicate was immediately perceived as an ideal solution to these limitations. 

V and Sn-modified mesoporous silicates were reported to be active in a number of liquid phase oxidation reactions. Ti-containing samples were used for the selective oxidation of large organic molecules in the presence of te/t-butyl hydroperoxide (TBHP) or dilute H2O2 [71,136,137,139-141,147,186,237]. Typical data shown in Table 5 indicate that both Ti-MCM-41 and Ti-HMS are efficient cat ysts for the epoxidation of bulky olefins such as a-terpineol and norbomene in the presence of TBHP or H2O2. Comparison with H-B indicates that the accessibility of active sites plays a critical role in the liquid phase oxidation of organic molecules. Mesoporous titanosilicates also exhibited remarkable activity in the hydroxylation of 2,6-di-rerr-butyl phenol (2,6 DTBP) [142,147] and the oxidation of cyclododecanol [147], naphthol [147] aniline [237] and chloroaniline [186]. However, they were disappointingly poor catalysts for the liquid phase oxidation of n-hexane and aliphatic primary amines, as well as the ammoximation of cyclohexanone [147,238]. 

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