Silicoaluminophosphate molecular sieves

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. 

Hydrothermal Stability and Cracking Behavior of Silicoaluminophosphate Molecular Sieve-37 with Different Silicon Contents... 

The catalytic activity of silicoaluminophosphate molecular sieves (SAPO-5, SAPO-11, SAPO-34) has been studied during propylene conversion. During die reaction, SAPO-34 and SAPO-5 yielded C2-C7 hydrocarbons but both catalysts deactivated severely during reaction. The initial activity of SAPO-34 which contained sites of stronger acidity was higher than SAPO-5. SAPO-11, showing lower activity than SAPO-5 and SAPO-34 as well as rapid deactivation, yielded only C6 hydrocarbons. Differences in the product distribution observed during both reaction studies arise from the different acidity, pore structure and pore size of the S APO molecular sieves. 

Silicoaluminophosphate molecular sieves (or SAPO-s) have negatively charged frameworks which give them cation exchange capacity and weak-to-mild acidity. 

It proved to be possible to identify ordered Si-O-Al environments in molecular sieves by 27Al -29Si REAPDOR (i.e. rotational echo adiabatic passage double resonance) NMR techniques.350 NMR studies have been reported for the following silicoaluminophosphate molecular sieves SAPO-5 351 SAPO-11 and -31 352,353 H-SAPO-34 and -37 354 and SAPO-44.355... 

H.-L. Zubowa, E. Alsdorf, R. Fricke, F. Neissendorfer, J. Richter-Mendau, E. Schreier, D. Zeigan, and B. Zibrowius, Synthesis and Properties of the Silicoaluminophosphate Molecular Sieve SAPO-31. J. Chem. Soc., Faraday Trans., 1990, 86, 2307-2312. 

M. Hartmann L. Kevan (1999). Chem. Rev., 99, 635-663. Transition-metal ions in aluminophosphate and silicoaluminophosphate molecular sieves Location, interaction with adsorbates and catalytic properties. 

Lok B M, Messina C A, Patton R L, Gajek R J, Cannon T A and Flanigen E M (1984), Silicoaluminophosphate molecular sieves another new class of microporous crystaHine inorganic solids , J Am Chem Soc, 106, 6092. 

Studies with silicoaluminophosphate molecular sieves showed that SAPO-37 (faujasite geometry) and SAPO-5 (API structure) were good catalysts for the transformation of pinacol, with selectivity increasing with reaction time (batch reactor, 423 K) [31]. In contrast, the activity of two other samples (SAPO-11 and SAPO-34) was inferior, possibly because inadequate pore dimensions hindered access of the reacting pinacol to the active sites. 

S. J. Miller, Catalytic Dewaxing Process Using a Silicoaluminophosphate Molecular Sieve, U.S. Patent 4,859,311. 

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. 

Dehydroisomerization of /t-butane to isobutene over Pd modified silicoaluminophosphate molecular sieves... 

Coke formation has only been studied for H-SAPO-34 catalyst materials and not for H-ZSM-5 zeolites by means of in situ MAS NMR and UV-vis spectroscopies. Thus, catalyst deactivation is discussed for this particular silicoaluminophosphate molecular sieve on the basis of the results shown in Figure 12.19. By adding the capability of in situ UV-vis spectroscopy to the in situ continuous flow MAS... 

As with methanol ammoxidation, yield and selectivity to the nitrile product are relatively high compared to ammoxidation of an alkene or alkane substrate. Using alumina-supported V-P-Sb-0 catalysts, selectivity to acetonitrile of 96% is obtained at 84% conversion of ethanol (81% acetonitrile yield) at 400°C (101), whereas a silicoaluminophosphate molecular sieve gives a reported 99% yield of acetonitrile at complete conversion of acetonitrile at 350°C (102). Both catalysts possess a relatively high level of surface acidity, mainly because of the presence of phosphorus and aluminum oxide moieties. These are expected to promote the initial step of the reaction—surface alkoxy formation by, for example, an equilibrium with surface hydroxyl groups. 

The catalytic activities of silicoaluminophosphate molecular sieves for propene... 

Djieugoue M-A, Prakash AM, Kevan L. Catalytic study of methanol-to-olefms conversion in four smaU-pore silicoaluminophosphate molecular sieves the influence of the structural type, nickel incorporation, nickel location, and nickel concentration. J Phys Chem B 2000 104 6452-61. 

Janke, C., Schneider, M., Bentrup, U., Radnik, J., Martin, A., Scholz, G., and Brilck-ner, A. Impact of phosphorus and nitrogen on structure and catalytic performance of VZrPON oxynitrides in the ammoxidation of 3-picohne. J Catal 111, 196-207 (2011). Srinivas, N., Radha Kishan, M., Kulkami, S. J., and Raghavan, K. V. Ammoxidation of picolines over modified silicoaluminophosphate molecular sieves. Microporous Mes-opomusMater 39, (2000) 125-134. 

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