Molecular aluminophosphate

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. 

There are numerous stmctures that are similar to 2eofites, such as aluminophosphate molecular sieves, AlPOs, but these have not found catalytic apphcations. Zeofites can be modified by incorporation of cations in the crystalline lattice which are not exchangeable ions, but can play catalytic roles. For example, sificahte, which has the stmcture of ZSM-5 but without Al, incorpora ting Ti in the lattice is a commercial catalyst for oxidation of phenol with H2O2 to give diphenols the catalytic sites may be isolated Ti cations (85). 

The liquid-phase autoxidation of cyclohexane is carried out in the presence of dissolved cobalt salts. A lot of heterogeneous catalysts were developed for this process but most catalysts lacked stability. The incorporation of cobalt ions in the framework of aluminophosphate and aluminosilicate structures opens perspectives for heterogenization of this process. CoAPO (cobalt aluminophosphate) molecular sieves were found to be active heterogeneous catalysts of this oxidation.133 Site isolation was critical to get active catalysts.134... 

Aluminophosphate-Based Molecular Sieves In 1982 a major discovery of a new class of aluminophosphate molecular sieves was reported by Wilson et al. [26]. By 1986 some 13 elements were reported to be incorporated into the aluminophosphate frameworks Li, Be, B, Mg, Si, Ti, Mn, Fe, Co, Zn, Ga, Ge and As [27]. These new generations of molecular sieve materials, designated AlP04-based molecular sieves, comprise more than 24 structures and 200 compositions. 

The characteristics of aluminophosphate molecular sieves include a univariant framework composition with Al/P = 1, a high degree of structural diversity and a wide range of pore sizes and volumes, exceeding the pore sizes known previously in zeolite molecular sieves with the VPI-5 18-membered ring material. They are neutral frameworks and therefore have nil ion-exchange capacity or acidic catalytic properties. Their surface selectivity is mildly hydrophilic. They exhibit excellent thermal and hydrothermal stability, up to 1000 °C (thermal) and 600 °C (steam). 

The introduction of silicon into hypothetical phosphorus sites produces negatively charged frameworks with cation-exchange properties and weak to mild acidic catalytic properties. Again, as in the case of the aluminophosphate molecular sieves, they exhibit excellent thermal and hydrothermal stability. 

Flanigen, E.M., Lok, B.M., Patton, R.L, and Wilson, S.T. (1987) Aluminophosphate molecular sieves and the periodic table, in New Developments in Zeolite Science and Technology, Proc. 7th Inti. Zeolite Conf, Tokyo, 1986 (eds Y. Murakami, A. Ijima, and J.W. Ward) Elsevier, Amsterdam, pp. 103-112. 

The crystal structures of several metal aluminophosphate molecular sieves, in Innovation Zeolite Mater. Sci. (eds P.J. Grobet, W.J. Mortier, E.F. Vansant, and G. Schulz Eklofi), Stud. Surf. Sci. Gatal., vol. 37, Elsevier, Amsterdam, pp. 269-279. 

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. 

Heat-up rate effects have been investigated with respect to microwave synthesis of AlPO phases, however there are few publications concerning the heat-up effects in conventional heating [58]. There has also been at least one study of pH and H2O level on aluminophosphate crystallization [59]. A recent paper attempts to study the unique crystallization process of several aluminophosphate molecular sieve compositions [60]. 

Chemical Interactions of Aluminophosphate Molecular Sieve with Vanadium Oxide... 

The aluminophosphate molecular sieve, AIPO4-5, itself has limited potential as catalyst, since its stnjcture is neutral and has neither catbn exchange capacities nor acidity [1-3]. There are two possibilities for utilizing the molecular sieves one is rrwdification of the framework by substitution of metal atoms such as silicon [3-6] and/or transition metals [5-11], and the other is introducing active site by impregnation. 

The aluminophosphate molecular sieves have an interesting property for potential use as catalyst supports, due to their excellent thermal stabilities and unique structures. AIPO4-5 is known to retain its structure after calcination at 1000°C and have uni-directional channels with pore size of 8 A bounded by 12-membered rings [2]. To utilize molecular sieves as catalyst support, chemical interactions between the molecular sieve and active component, chemical stabilities, and surface structures must be determined. However, iittle attempt has been made to clarify the surface structures or properties of catalytically active components supported on the aluminophosphate molecular sieves. 

Aluminophosphate molecular sieves with uniformly sized pores are a new porous material composed of A1P04 and called ALPO. Recently much attention has been... 

S. Feng and T. Bein, Vertical aluminophosphate molecular sieve crystals grown at inorganic-organic interfaces. Science 265, 1839-1841 (1994). 

Catalysis. - Aluminophosphate molecular sieves (A1PO) form a family of synthetic zeotypes, containing many three dimensional framework structures. Metal substituted aluminophosphates (MAPO) have important applications as catalysts and HFEPR has been used to determine the catalytically active sites. Two very detailed papers on various MAPO have been reported recently22,23 using both echo-detected HFEPR at 95 GHz and 3H and 31P ENDOR. 

Both piperidine and pyridine serve as structure-directing agents in the commercial production of Ferrierite zeolite. More recently, use of DMAP has allowed preparation of novel metallo-aluminophosphate molecular sieves with both small- <2006W02006037437> and large-pore architecture <2006USA074267>. 

Pd-containing aluminophosphate molecular sieves have been used to carry out crossed aldol condensations between an aldehyde and a ketone by using a 0.5 % Pd/ MnAPSO-31 catalyst in a vapour-phase fixed bed reactor.[14] Thanks to the excess of the ketone with respect to the aldehyde (4 1), it is possible to get high selectivity to the desired product, i.e. 70 % of heptan-2-one from n-butyraldehyde and acetone and 89 % of pentan-2-one from acetaldehyde and acetone, the major by-product being, in both cases, MIBK from acetone self-condensation. 

We report here, for the first time, the synthetic procedures used to crystallize the aluminophosphate molecular sieve VPI-5. Two synthesis methods are illustrated. The step by step procedures are discussed in detail and reveal the precise nature of synthesizing VPI-5. 

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