Aluminophosphates structure

Tang et al.84,85 also examined the incorporation of MMT in intumescent PP with a compatibilizer (hexadecyltrimethylammonium bromide) which is usually used as surfactant for making OMMT. Evidence of making a nanocomposite is shown with and without the intumescent system. Cone calorimetry shows a large improvement in the flammability properties when using OMMT. The results are similar to what we showed above. They postulated a mechanism of action suggesting the formation of an aluminophosphate structure but no evidence was given. 

According to this equation, Xu and coworkers developed a method to generate hypothetical open-framework aluminophosphate structures with specified Al/P stoichiometry using the automated assembly of SBUs.[76] For each specified Al/P stoichiometry, all the possible combinations of A1 and P atoms with different coordination states could be calculated according to Equation (3.2). The A1 and P atoms of different coordination states, together with the clusters constructed by them, could be selected as the building... 

Y. Li, J.H. Yu, J.X. Jiang, Z.P. Wang, J.N. Zhang, and R.R. Xu, Prediction of Open-framework Aluminophosphate Structures using the Automated Assembly of Secondary Building Units Method with Lowenstein s Constraints. Chem. Mater., 2005, 17, 6086-6093. 

Prediction of Open-framework Aluminophosphate Structures by using the AASBU Method with Lowenstein s Constraints... 

All the possible combinations of different kinds of Al and P atoms can be calculated for a specified stoichiometry. Here the prediction of open-framework aluminophosphates with AlgP1004o stoichiometry is taken as an example. For instance, 6 Al(Ob)4, 2 Al(Ob)s, 4 P(Ob)4, and 6 P(Ob)3(Ot) atoms could be a possible combination for an aluminophosphate structure with such a stoichiometry. Assuming a space group with two symmetric operations, such as space group P-1, only half of the atoms, i.e., 3 Al(Ob)4, 1 Al(Ob)s, 2 P(Ob)4 and 3 P(Ob)3(Ot) atoms, are needed to be introduced in the asymmetric unit. All the building units used in this example are shown in Figure 7.15 together with the labels... 

Figure 7.15 The building units for the generation of aluminophosphate structures with 6 At (Ob) 4, 2 At(Ob)s, 4 P(Ob)4, and 6 P(Ob)3(Ot) atoms in a unit cell. The lighter polyhedra denote the ATcentered polyhedra the darker tetrahedra denote the P-centered tetrahedra. Reproduced with permission from [39]. Copyright (2005) American Chemical Society...

This method will not only aid the prediction of hypothetical aluminophosphate frameworks, but also serve as a tool to set up the initial structural models for the solution of unknown aluminophosphate structures. 

One-, two-, and three-dimensional aluminophosphate structures have been prepared. An infinite chain anion is found in M0OAIP2O8 which is isomorphous to VOP2SiOg, with Al replacing Si in the anion (8). Sheet anions such as Al2P30i2 and Al3P40i6 have been prepared hydrothermally using various alkylammonium templates which lie between the layers. 

Figure 2.17 The large pore (12MR) aluminophosphate structures (top left) AIPO4-5 and (top right) AIPO4-36 and the extra large pore (18MR) VPI-5 (below) possess one-dimensional channel systems. In the as-prepared VPI-5 (shown) aluminium exists in both tetrahedral and octahedral coordination, the octahedral coordination being made up by two coordinated water molecules.

P(4) A1 P 2 D INEPT experiment unambiguously identifies a resolved P signal in the spectrum. This study underlines what details of connectivity and internuclear distances can now be obtained from complex but well-ordered aluminophosphate structures. 

Studies of this type have shown that incorporation of magnesium into the CHA aluminophosphate structure can be random, within the Af site. In the aluminophosphate form of sodalite, (AlPO-20) magnesium substitutes in an ordered way for aluminium, and Barrie and Klinowski interpret the observed P NMR intensities in terms of an ordered distribution where there are never two magnesium cations in the same 4MR. ... 

The hexagonally ordered mesostructured aluminophosphate structure was also reported to form in an alcoholic system, which, however, collapsed upon heating (140). Kieser and co-workers proposed a general route to homogeneous. 

Table 10. Structural Parameters of the First Coordination Shell around Fe Atom in the Template-Free Microporous and Mesoporous Iron-Modified Aluminophosphate Structures...

Tables from 5 to 14 show, that the substitution of Al + and/or P + by divalent metal ions or tetravalent silicon in aluminophosphate structures creates both the Br0nsted and Lewis acid sites. These acid sites differ mutually in their donor-acceptor ability. The first one can transfer protons from the catalyst to the adsorbed molecules, whereas the latter can accept an electron pair from the adsorbed molecules. The strength and concentration of both types of acid sites determine the activity, selectivity, and lifetime of catalysts in acid-catalyzed reactions. The acid strength varies among aluminophosphates, and it is mainly dependent on the type of metal substituted in the framework. Also the catalytic performance is affected by structural characteristics of the framework such as the pore size, pore shape, or geometry.

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