Zeolites silicoaluminophosphates

The silicoaluminophosphate (SAPO) family [30] includes over 16 microporous structures, eight of which were never before observed in zeolites. The SAPO family includes a silicon analog of the 18-ring VPI-5, Si-VPI-5 [31], a number of large-pore 12-ring structures including the important SAPO-37 (FAU), medium-pore structures with pore sizes of 0.6-0.65 nm and small-pore structures with pore sizes of 0.4-0.43 nm, including SAPO-34 (CHA). The SAPOs exhibit both structural and compositional diversity. 

Up to now, a variety of non-zeolite/polymer mixed-matrix membranes have been developed comprising either nonporous or porous non-zeolitic materials as the dispersed phase in the continuous polymer phase. For example, non-porous and porous silica nanoparticles, alumina, activated carbon, poly(ethylene glycol) impregnated activated carbon, carbon molecular sieves, Ti02 nanoparticles, layered materials, metal-organic frameworks and mesoporous molecular sieves have been studied as the dispersed non-zeolitic materials in the mixed-matrix membranes in the literature [23-35]. This chapter does not focus on these non-zeoUte/polymer mixed-matrix membranes. Instead we describe recent progress in molecular sieve/ polymer mixed-matrix membranes, as much of the research conducted to date on mixed-matrix membranes has focused on the combination of a dispersed zeolite phase with an easily processed continuous polymer matrix. The molecular sieve/ polymer mixed-matrix membranes covered in this chapter include zeolite/polymer and non-zeolitic molecular sieve/polymer mixed-matrix membranes, such as alu-minophosphate molecular sieve (AlPO)/polymer and silicoaluminophosphate molecular sieve (SAPO)/polymer mixed-matrix membranes. 

VII. Investigations of Chemical Behavior and Local Structure of Surface Sites in Zeolites and Microporous Silicoaluminophosphates... 

Among the early investigations of methanol adsorption and conversion on acidic zeolites, most of the H and C MAS NMR experiments were performed under batch reaction conditions with glass inserts in which the catalyst samples were fused. Zeolites HZSM-5 76a,204,206,264-272), HY 71,72), H-EMT 273), HZSM-12 274), HZSM-23 275), H-erionite 275), H-mordenite 271,272), and H-offretite 275,276), silicoaluminophosphates H-SAPO-5 271,274), H-SAPO-11 274), and H-SAPO-34 76,277,278), as well as montemorillonite 279) and saponite 279) were investigated as catalysts. 

More recently phosphorus-containing zeolites developed by Union Carbide (alu-minophosphates, silicoaluminophosphates) were shown to be equally effective in methanol condensation.439-444 ZSM-5 was also shown to exhibit high activity and selectivity in the transformation of Fischer-Tropsch oxygenates to ethylene and propylene in high yields.445 Silicalite impregnated with transition-metal oxides, in turn, is selective in the production of C4 hydrocarbons (15-50% isobutane and 8-15% isobutylene).446... 

Other elements, such as Ga and Ge, can substitute for Si and A1 in the zeolitic framework, and there are claims that many other elements can also do so. New classes of nonsilicate zeolite-type crystalline aluminophosphates (31) and silicoaluminophosphates (SAPO) (65) have been reported but relatively little is known about their chemical behaviour. 

Silicoaluminophosphates (SAPO s) (1) are molecular sieves which contain tetrahedra of oxygen surrounded silicon, aluminum, and phosphorus. These microporous solids not only exhibit properties characteristic of zeolites but also show unusual physiochemical traits ascribable to their unique chemical compositions (1,2). 

The entrapment-type nanocomposites can be prepared from zeolites and they are of two types zeolite-inorganic and zeolite-organic. Zeolite crystals are three-dimensionally linked network structures of aluminosilicate, aluminophosphate (ALPO), and silicoaluminophosphate (SAPO) composition and are porous, the pores being in the range of 2.8 to 10 A. Many of the highly siliceous, ALPO, and SAPO zeolites have been synthesized using organic templates such as tetrapropyl... 

Raman spectroscopy was used to characterise molecular sieves Na2Nb2 x Mx06 x(0H)x.H20, where M = Ti or Hf, x < 0.2, and the parent compound Na2Nb206.H20.59 Ab initio calculations were reported on the vibrational wavenumbers for the titanium-containing zeolite titanium affretite.60 Raman spectra of titanium-aluminophosphate and -silicoaluminophosphates gave evidence on the coordination environment of titanium(IV) centres.61... 

The commercial importance and diverse uses of zeolites have long prompted attempts to synthesise related compounds. Many framework materials containing atoms other than silicon and aluminium are now known. These materials, known as zeotypes , are not zeolites in the strictest sense as they are not aluminosilicates. Examples include the aluminophosphates, commonly known as AlPOs (Wilson et al., 1982), silicoaluminophosphates - SAPOs (Lok et al., 1984) - and gallophosphates - GaPOs (Parise, 1985). 

It has been reported by F.A. Mumpton (1978) that more than 1000 occurrences of zeolite minerals in over 40 countries have been discovered since 1950. In addition to the hydrated aluminosilicate species, new minerals related to zeolites have been discovered, including the porous clathrasUs such as Melonophlogite (a silica only framework). Species in which the aluminum or silicon has been replaced by other elements (such as phosphorus, iron, and beryllium) have also been discovered as exemplified by viscite, a silicoaluminophosphate related to analcime. At the present there are 38 different natural framework topologies, as shown in Table 25. 

However, the incorporation of metal cations whose valence is different from that of A1 or P leads to the formation of electronically unsaturated sites, as schematically shown in Figure 3. This addition of aliovalent metal cations into the lattice of AlPO-n generates solid acidity and ion-exchange sites. There are numerous reports on the incorporation of many different metal cations into the lattice of AlPO-n. Table 2 summarizes the reported isomorphous substituted AlPO-n. The family of AlPO-n substituted with metal cations is generally called metal aluminophosphates (MeAPO-n). The typical metal cations substituted into AlPO-n are Li, B, Be, Mg, Ti, Mn, Fe, Co, Zn, Ga, Ge, Si, and As. The Si-substituted AlPO-n is called a silicoaluminophosphate and denoted as SAPO-n, where n also means the framework structure, and it is distinct from the MeAPO-n materials.SAPO-n exhibits both structural diversity and compositional variation. In particular, the crystal structure of SAPO-n is of greatest interest, because the distribution of the Si atom in the framework is quite complicated. Some crystal structures, such as SAPO-40, are only found in SAPO-n and not in AlPO-n or zeolite. The mole... 

Intermediates in high-temperature processes have been stabilized at low temperature after y irradiation of metal oxides and zeolites. Important early examples were oxygen anions. O, 02 and O. Some of their reactions with small molecules were also elucidated by EPR. Metal cluster ions have also been produced by radiolysis and stabilized in zeolites. Examples include alkali metal cation clusters in faujasites and silver cation clusters in zeolite A and in silicoaluminophosphate molecular sieves. Detailed information was obtained from EPR studies about their structure, thermal stability and formation of adducts. 

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