Aminated aluminophosphates

Scheme 2.4 Pictorial Illustration of the Synergy Observed when Acid and Basic Sites are Simultaneously Present in Aminated Aluminophosphates, Derived from Simultaneous Activation...

To evaluate properties of basic catalysts, the Knoevenagel condensation over aluminophosphate oxynitrides was investigated [13]. In this reaction usually catalysed by amines, the solid catalysts function by abstraction of a proton from an acid methylene group, which is followed by nucleophilic attack on the carbonyl by the resultant carbanion, re-protonation of oxygen and elimination of water. The condensation between benzaldehyde and malononitrile is presented below. 

Similarly, reactive oxide mixtures are also used to synthesize aluminophosphate molecular sieves, usually starting from phosphoric acid along with the addition of alumina and silica sources analogous to those used in zeolite synthesis with a notable exception alkylammonium salts and amines were ultilized in structure-direchng and space filling to the exclusion of alkali hydroxide solutions and alkali metal salts. 

The extensive size of organic amine as structure-directing templates or pore filling agents, coupled with a new gel chemistry resulted in the discovery of a third generation of zeolites containing Al3+ and P5+ as lattice atoms (1982). These aluminophosphate materials are a family of molecular sieves as shown in figure 7.10. 

The amount of water present during the synthesis of large AFI-type aluminophosphate crystals was found to be of significant importance. However, yield of AlP0 -5 and crystal size were countercurrently influenced. It follows tnat at least with tripropyl amine, either few large crystals or maximum conversions into small particle AlP0 -5 is possible. 

Zeolites and related aluminosilicates constitute a vital family of microporous materials with immense applications in catalysis, sorption and separation processes [1-3]. The discovery of aluminophosphates is an important landmark in the science of these materials [4], All these materials are, in general, synthesized under hydrothermal conditions by making use of template molecules [2]. The template molecules are usually organic amines and they are involved in the formation of these framework structures in more ways than one. While it is difficult to pinpoint the exact manner in which the amines participate or direct the formation of these inorganic structures, it is generally believed that their size and shape are crucial in determining the pore structure. In recent years, a variety of open-framework structures formed by divalent metal phosphates... 

The three-dimensional structures are characterized by the presence of channels and voids where the structure-directing amine molecules usually reside. In many of the aluminophosphates it has been possible to remove the amine... 

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 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. ... 

Sayari et al. [209-212] followed another path to the synthesis of mesolamellar aluminophosphates. They used AI2O3, H3PO4 and primary or tertiary amines as surfactants in aqueous media. The surfactant was found to be protonated while acting as template. Effects of synthesis parameters such as Al/P, P/amine, P/H2O ratios were studied systemically by XRD and Al and P NMR. The connectivity between Al and P was found to be dependent on the synthesis parameters. 

Aluminophosphate A1PQ4 5. AlPO -5 was obtained from compositions containing pseudoboehmite (Pural SB, Condea) which was added to aqueous phosphoric acid (Merck, 85%) and deionized water. Finally, tripropyl amine (Aldrich) was continuously added to the stirred solution. The crystallization time was limited to 72 hours. 

Synthesis of large AFI-tvpe crystals. For these studies of the crystallization of large AFI-type aluminophosphate crystals, the reaction temperature T, the concentration of tripropyl amine Pr3N, and the amount of water were chosen as operational variables. Synthesis runs were performed with each of these "factors" at a high (+) and a low (-) level, for molar compositions with b Pr3N - A1203 - P2O5 - c H20 as indicated in Table I ... 

Similarly, as shown in Figure 3.21 (b), (c), (d), and (e), there exists an excellent linear correlation between the charge/volume of the charged species encapsulated in the framework and the charge density of the anionic framework for the anionic aluminophosphates with Al/P ratio of 1/2 directed by arylamines, the anionic aluminophosphates with Al/P ratio of 2/3 directed by cyclic amines, the layered anionic aluminophosphates with Al/P ratio of 3/4 and 4,6,8-net topological sheet structure directed by chain-shape alkylamines, and the layered anionic aluminophosphates with Al/P ratio of 3/4 and 4,6,12-net topological sheet structure directed by chain-shape alkylamines as well. 

Table 5.14 Organic amines and corresponding aluminophosphate molecular sieves...

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