Microporous aluminophosphates

Electron Spin Resonance Spectroscopy. Several ESR studies have been reported for adsorption systems [85-90]. ESR signals are strong enough to allow the detection of quite small amounts of unpaired electrons, and the shape of the signal can, in the case of adsorbed transition metal ions, give an indication of the geometry of the adsorption site. Ref. 91 provides a contemporary example of the use of ESR and of electron spin echo modulation (ESEM) to locate the environment of Cu(II) relative to in a microporous aluminophosphate molecular sieve. 

The past nearly six decades have seen a chronological progression in molecular sieve materials from the aluminosilicate zeolites to microporous silica polymorphs, microporous aluminophosphate-based polymorphs, metallosilicate and metaHo-phosphate compositions, octahedral-tetrahedral frameworks, mesoporous molecular sieves and most recently hybrid metal organic frameworks (MOFs). A brief discussion of the historical progression is reviewed here. For a more detailed description prior to 2001 the reader is referred to [1]. The robustness of the field is evident from the fact that publications and patents are steadily increasing each year. 

Beale, A.M. and Weckhuysen, B.M. (2007) Understanding the crystallisation processes leading to the formation of microporous aluminophosphates, in Zeolites to Porous Materials-The 40th Anniversary of International Zeolite Conference, Studies in Surface Science and Catalysis, vol. 170, Elsevier Science Publishers B V, Amsterdam,... 

Corma [208] and Dutta [209] and their coworkers reported the photocyclization of azobenzene in zeolite HY and microporous aluminophosphate, respectively. They also demonstrated that the acid groups in these media directly intervene in the photochemical reactions of azobenzene. 

Crystalline microporous aluminophosphates containing framework metals, that is, MeAPO, constitute an interesting group of molecular sieves [29,137], These materials are synthesized hydrothermally between 100°C and 250°C using organic templates, and crystallize into different structure types. 

A novel class of crystalline, microporous aluminophosphate phases has been discovered. It represents the first class of molecular sieves with framework oxide compositions free of silica. The new class of materials encompasses some fourteen reported three-dimensional microporous framework structures, and six two-dimensional layer-type structures. The three-dimensional structures include structural analogues of the zeolites sodalite and erionite-offre-tite. The novel phases can be synthesized hydro-thermally in the presence of organic amines and quaternary ammonium templates. The template is entrapped or clathrated within the crystallizing aluminophosphate network. After thermal decomposition of the template the three-dimensional molecular sieves have the general composition of Al303 1.0 ... 

The first breakthrough was provided by Flanigen et al. [7] who, playing on the similarity 2 Si4+ -o-A13+ -f P5+, synthesized microporous aluminophosphates (hereafter noted AlPOs) with structures related to those of zeolites. The structural studies [8] showed however a striking difference between the two families. As already mentioned, the framework of zeolites is built up exclusively from connected tetrahedra which can accept small amounts (<10% of substitution) of other metals, whereas in aluminophosphates and homologous gallophosphates, Al and Ga polyhedra can adopt five and sixfold coordinations, which change [9] the connectivity of the framework, and therefore the shape of the windows. 

The products of such reactions depend upon the pressure, temperature, pH, phosphate, and cation concentrations, and may be difficult to predict or rationalize. For example, the equation (3) produces an acid phosphate and a phosphate hydroxide. Microporous aluminophosphates and related phases (see Section 5.1.2) are prepared in hydrothermal bombs using hydrated cations or molecular templates such as organic amines or ammonium cations to direct the porous framework. Many new structures with metal phosphate chains, layers, or three-dimensional networks have been prepared hydrothermally in recent years, for example, templated vanadium phosphates and iron phosphates. ... 

Usefiil zero thermal expansion composites are made by combining materials that show the unusual property of negative thermal expansion (i.e. contraction) with normal (positive) expansion materials. Examples of phosphates showing negative thermal expansion are the diphosphate-divanadate solid solutions ZrP2- V Oy and the microporous aluminophosphate AIPO-17 which shows a particularly large effect. ... 

Table 21.1 Oxidation of aromatic and aliphatic alcohols to their corresponding aldehydes and ketones using a microporous aluminophosphate catalyst and TS-1 in combination with APB... 

Fig. 7 Sheared 3QMAS NMR spectrum of microporous aluminophosphate AlPO-40 recorded at 9.4 T. The lengths of the first and second hard pulses were 2.5 ps and 0.8 ps, (Ri=100 kHz). The soft pulse kHz) length was 9 ps. 200 data points (240 transients...

In 1982, Wilson, Lok, and Flanigen et al. successfully synthesized a novel family of molecular sieves, that is, microporous aluminophosphates A1P04-w.[6] The discovery of A1P04-w is regarded as a milestone in the development of porous materials. Not only... 

Hydrothermal synthesis of microporous compounds in the presence of fluoride source refers to the hydrothermal or solvothermal crystallization of aluminosilicate zeolites or microporous aluminophosphate such as AlP04-n series in the presence of a fluoride source. The successful introduction of fluoride ion into the hydrothermal or solvothermal synthesis of microporous materials paves the way for the introduction of other complex-ion or chelation agent s to the hydrothermal crystallization of microporous compounds. 

Synthesis of Microporous Aluminophosphates and other Metal Phosphates in the Presence of Fluoride Source... 

Nearly all syntheses of zeolites and microporous aluminophosphates have limitations to gel composition and other parameters. For example, some zeolites with special compositions such as high-silica Y zeolite and low-silica ZSM-5 cannot be directly synthesized. A secondary framework modification is necessary for their preparation. For instance, dealuminization, isomorphous substitution of extraneous silicon for aluminum, and removal of the sodium process in Y zeolite are necessary to prepare ultra-stable zeolite Y (USY) isomorphous replacement of framework atoms of boron with aluminum in a presynthesized silicon-boron structure is often used to prepare some specific aluminosilicate zeolites that cannot be directly synthesized, such as Al-SSZ-24 (AFI) and Al-CIT-1. Secondary synthesis (post-treatment) will be discussed in detail in Chapter 6. 

Because most of the microporous open structures are metastable thermodynamically, many zeolites and microporous aluminophosphates can transfer to more stable structures under heating, which can be used to prepare some specific zeolite structures. For example, boron-substituted zeolite [> was used to prepare boron-substituted microporous SSZ-24 via crystal transition. 

In addition to pure-silica zeolites, titaniumsilicates such as TS-1 and TS-2, Ti-BEA, borosilicates, zincosilicates, and microporous aluminophosphates can be synthesized by using the DGC (SAC) method as well/1061... 

Commonly used aluminum sources in the synthesis of zeolites include sodium aluminate (NaA102, Na20 54%), pseudo-boehmite, home-made aluminum hydroxide, and aluminum isopropoxide, which is the mostly used in the synthesis of microporous aluminophosphates. The structures of the two most important aluminum sources are shown in Figure 5.11 and Figure 5.12, respectively. 

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