Pore size, aluminophosphate

Table IV. m-Xylene/Ethylbenzene Reactions with Medium Pore Size Aluminophosphate Based Molecular Sieves...

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 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. 

The most obvious approach to obtain controlled mesoporosity is the extension of zeolite-like three-dimensional framework structures to larger pore-sizes. Zeolite-like compounds in the micro- and mesoporous range are the aluminophosphate VPI-5, cloverite and ULP (MCM-41). These new materials are characterized by pore diameters between 1.3 nm and 20 nm. 

P30s. The various structures exhibit intracrystalline adsorption pore volumes from 0.04 to 0.35 cm3/g, and pore sizes from 0.3 to 0.8nm. The aluminophosphate frameworks are hydrophilic. 

The most common kind of porous materials are the ones possessing a disordered or random porous network [1,2]. In this class of solids belong various silicas [3] aluminas [4] aluminophosphates [5] as well as a large number of aluminosilicate solids encountered in geological forms [6]. The pore size distribution of such disordered or random porous materials is usually characterized on a routine basis by N2 adsorption at 77K. From such measurerrient the following characteristic parameters of porous solids can be calculated ... 

P.A. Barrett and R.H. Jones, The Pore-size Modification of a Layered Aluminophosphate [A13P4016C9H24N3] by Rational Selection of the Intercalated Template Cation. J. Chem. Soc., Chem. Commun., 1995, 1979-1980. 

A large family of novel aluminophosphate based molecular sieves has recently been described in the literature(l-3). The individual crystal species of these molecular sieves represent a wide variety of crystal structures and chemical compositions. Structures include several novel crystal types and various intracrystalline pore sizes. Thus aluminophosphate-based molecular sieves have been... 

The present paper reports on the catalytic properties of selected aluminophosphate molecular sieves in model hydrocarbon reactions. The molecular sieves were selected to represent large and medium pore sizes with a variety of framework elements including transition metals, in addition to aluminum and phosphorus. Model reactions were chosen to explore catalytic performance in paraffin, olefin and aromatic rearrangement reactions to probe molecular sieve character, shape selectivity and catalytic activity, particularly for reactions involving olefins or olefin reaction intermediates. 

Cfi Aromatic Reactions Without Hydrogen. In the present study, tire aluminophosphate molecular sieves have been used alone and with added platinum and hydrogen to isomerize Cs aromatic feeds. In an initial screening study, a series of large to medium pore size molecular sieves were evaluated for catalytic activity for m-xylene rearrangements at 1000° F without added metal and hydrogen. 

Iron substituted aluminophosphate molecular sieves (Fe-AlP04-l 1, Fe-AlP04-5 and Fe-VPI-5) are catalytically active in oxidations of aromatic compounds such as hydroxylation of phenol, benzene, and naphthol, as well as epoxidation of styrene. Catalytic data show that the activities of Fe-AlP04-l 1, Fe-AlP04-5 are comparable with that of TS-1 in the oxidation of aromatic compounds. Furthermore, Fe-VPI-5 shows high activity in naphthol hydroxylation by H2O2, while TS-1 is completely inactive due to the small pore size. By comparison of various catalysts, Fe (III) in the framework is considered to be the major active site in the catalytic reactions. 

Microwave heating has also been used to prepare other molecular sieves such as aluminophosphate aud silicoaluminophosphate materials. A comparison between conventional and nticrowave heating in the syntheses of SAPO-11 has been performed, with particular phasis on study effects on nncleation and crystal growth. Both were enhanced nsing microwave heating, narrower pore size distributions and more uniform crystal morphologies being observed. 

Extra-large-pore zeolites (at least 14-membered rings with pore sizes around 1.0 nm)—e.g., aluminosilicates CIT-5, UTD-1. aluminophosphates (VPI-5, JDF-20, gallophosphate. cloverite). 

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