Extra-large micropore mesopore

As mentioned earlier in this chapter, it is the social demands and wide applications of porous materials that keep them under continuous exploration. From natural zeolites to synthesized ones, from low-silica zeolites to high-silica ones, from aluminosilicate molecular sieves to aluminophosphate-based ones, from extra-large microporous materials to mesoporous materials, and from inorganic porous frameworks to MOFs, together with newly emerging macroporous materials, all these porous materials have ordered and uniform porous systems. 

Design OF EXTRA-LARGE PORE ZEOLITES AND OTHER MICROPOROUS AND MESOPOROUS CATALYSTS 11... 

The inherent limitations of the use of zeolites as catalysts, i.e. their small pore sizes and long diffusion paths, have been addressed extensively. Corma reviewed the area of mesopore-containing microporous oxides,[67] with emphasis on extra-large pore zeolites and pillared-layered clay-type structures. Here we present a brief overview of different approaches to overcoming the limitations regarding the accessibility of catalytic sites in microporous oxide catalysts. In the first part, structures with hierarchical pore architectures, i.e. containing both microporous and mesoporous domains, are discussed. This is followed by a section on the modification of mesoporous host materials with nanometre-sized catalytically active metal oxide particles. 

Optimization of the synthesis of an ultra-large pore aluminophosphate VPI-5 using di-n-butylamine (n-DBA-VPI-5) has been done. The sample synthesized was characterized by XRD, SEM, FTIR, TGA-DTA, NMR and sorption studies. The extra-large pores (larger than lOA) in VPI-5 were confirmed by adsorption measurements. N2 adsorption at 77K shows mesopores with pore diameter of 36A alongwith the micropores of n-DBA-VPI-5. 

Since many properties of crystalline oxides, e.g., acidity, hydrothermal stability, etc., are the essential features exploited in commercial applications of these oxides, it is not unexpected that the ordered, mesoporous materials have not yet found much commerical use. The large void volumes, pore sizes and surface areas of the ordered, mesoporous materials provide advantages over microporous solids in certain areas of application but issues such as stability remain. Thus, if crystalline, extra-large pore solids could be prepared in the pore size and void volume ranges of the mesoporous materials, they would be immediately commercialized. The question remains as to why crystalline materials of this size range have not been synthesized. Navrotsky et al. have shown that pure silica, ordered, mesoporous silicas are energetically very close to pure silica, crystalline... 

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