Extra-large pore materials

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. 

Even though crystalline microporous materials include those with pore size between 10 and 20 A (called extra-large pore materials), few of them have a pore size within this range. This limits the applications of microporous materials to small molecules. There has always been a desire to increase the pore size of a crystalline material to more than 10 A while maintaining adequate thermal or hydrothermal stability required for various applications. Recent advances in chalcogenide and metal-organic framework materials have shown much promise for the preparation of extra-large pore materials. 

New materials that expand the microporous region of the zeohte are also interesting. In this group it is possible to find wide pore zeolite such as ITQ-21 which is accessible through six circular 0.74 nm openings [51], and extra-large-pore materials, like the phosphate-based VPI-5 or the more stable silicas UTD-1 and CIT-5 [52] with 0.8-1.2 nm openings. 

Keywords extra-large pore materials, ordered mesoporous materials,... 

Since the phosphate-based, extra-large pore materials do not reveal stability that is likely sufficient for many commercial applications, I will limit my discussions below to silica-based materials. As I have discussed elsewhere, the lack of stability in phosphate-based materials may not be due to the presence of extra-large rings, but rather to the nature of the structural units [9], With silica-based, extra-large pore materials, it appears that bulky structure directing agents will be required for their preparation. I will make this assumption in further discussions below. 

PL-3- Wednesday 8h30 - Evolution of extra-large pore materials M.E. Davis... 

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