Large pore molecular sieves incorporation

Unfortunately, the use of TS1 (as well as TS2 discovered in 1990 by the group of Ratnasamy (27)) in catalytic oxidations is restricted to the relatively small substrates able to enter the pores of these zeolites (apertures 0.55 nm). Therefore, many research groups attempted to incorporate titanium in large pore molecular sieves BEA zeolites, mesoporous molecular sieves MCM41 and MCM48. Other transition metal zeolites were also synthesized and tested in oxidation one of the main problems of these systems is the release of redox cations in liquid phase (24). Progress remains to be made to develop molecular sieves catalyzing the oxidation... 

Reddy et al. reported the synthesis of V-containing NCL-1 from a gel containing fumed sihca, NaOH, vanadyl sulfate and hexamethylene bis (triethyl-ammonium bromide). Incorporation of V is rather Hmited, the lowest Si/V ratio obtained being 150 [111]. Though the structure of NCL-1 is still unknown, adsorption and diffusivity experiments indicate a pore size close to that of mor-denite (ca. 7 A) [112]. Therefore, V-NCL-1 would represent the unique example of V incorporation in a large pore molecular sieve. 

The development of mesoporous materials with more or less ordered and different connected pore systems has opened new access to large pore high surface area zeotype molecular sieves. These silicate materials could be attractive catalysts and catalyst supports provided that they are stable and can be modified with catalytic active sites [1]. The incorporation of aluminum into framework sites of the walls is necessary for the establishment of Bronsted acidity [2] which is an essential precondition for a variety of catalytic hydrocarbon reactions [3], Furthermore, ion exchange positions allow anchoring of cationic transition metal complexes and catalyst precursors which are attractive redox catalytic systems for fine chemicals [4]. The subject of this paper is the examination of the influence of calcination procedures, of soft hydrothermal treatment and of the Al content on the stability of the framework aluminum in substituted MCM-41. The impact on the Bronsted acidity is studied. 

Our work on the alkylation of meta-diisopropylbenzene with propene over the acid form of various 12-member ring zeolites and molecular sieves shows that these catalysts can reveal shape selective behavior (39). As the effective size of the voids increases, the ratio of the formed 1,3,5- to 1,2,4-triisopropylbenzene increases e.g., mordenite and zeolite Y give 1.1 and 2.5, respectively. Additionally, an amorphous Si02/Al203 catalyst yields a ratio of 3.5. Thus, the smaller 12-ring materials show shape selective behavior. Based on these results, extra-large pore materials such as VPI-5 may show some shape selectivity for this reaction, if acid sites can be incorporated into the material. 

Similar to Ti-containing molecular sieves, an IR band at ca. 960 cm was also reported for [Si,V]MFI structures (cf., e.g., [340] and Volume 1, Chapter 7, pages 208-209, of the present series and references therein). Thus, Hongbin Du et al. [341] observed by the FTIR/KBr technique in synthesized large pore V-contain-ing zeolite Beta a band at 960 cm" and took the appearance of this signal as an indication of vanadium incorporation into the framework to produce H-[Si,Al,V]Beta. 

However, not all important phenomena of post-synthesis modification are covered with the present six chapters of Volume 3 of the series Molecular Sieves - Science and Technology . Topics such as, for instance, Incorporation of Dyes into Molecular Sieves , Preparation of Ship-in-the-Bottle Systems , Secondary Synthesis in Zeolites , Pore Size Engineering , Modification of Mesoporous Materials are equally important and, to a large extent, presently subject to very active research and development. Therefore, such topics will be dealt with in one of the subsequent volumes under the title Post-Synthesis Modification IT. 

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