Aluminophosphate molecular various

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. 

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. 

Aluminophosphates (A1P04) were discovered in 198248 and a large amount of research has been directed towards the incorporation of various elements into the framework of these molecular sieves 49 A particular area of study is the oxidation of primary and secondary alcohols to the corresponding carbonyl compounds, which are useful synthetic intermediates. Traditionally, alcohol transformations are performed with stoichiometric chromium(VI) reagents.50 However, due to environmental problems associated with chromium-containing effluent, attention has focused on the use of chromium in conjunction with oxidizing agents such as tert-butyl hydroperoxide.51 Sheldon and co-workers... 

Many new adsorbents have been developed over the past 20 years including carbon molecular sieves, new zeolites and aluminophosphates, pillared clays and model mesoporous solids. In addition, various spectroscopic, microscopic and scattering techniques can now be employed for studying the state of the adsorbate and microstructure of the adsorbent. Major advances have been made in the experimental measurement of isotherms and heats of adsorption and in the computer simulation of physisorption. 

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 synthesis of zeolites and zeolitic materials has been pursued for nearly 50 years (2), and the literature is filled with reports of structures, methods of preparation, and uses for these materials. The substitution of aluminum or silicon in the framework structure has been performed using many main group elements (3.41 as well as some transition metals (3.5). New families of molecular sieves which are based on an aluminophosphate framework have been reported recently, some of which are also microporous (6.7). Of the various new materials which have been reported, this review will focus on crystalline borosilicate molecular sieves. 

Regarding their use as cracking and isomerization catalysts, bulk oxides such as clays and amorphous silica-aluminas have been widely displaced by molecular sieve compounds (e.g., zeolites, aluminophosphates), whose well-defined pore structures generally offer higher selectivity and flexibility. Nevertheless, bulk oxides continue to be used for various cracking and isomerization applications in the petroleum industry. 

Aluminophosphates denoted as AlPO-n (n means the framework structure) are a new family of molecular sieves with unique zeolitic pore structure. Since the first report on the synthesis of AlPO-n by Wilson et al., synthesis of various types of AlPO-n as well as the isomorphous substitution of metal cation into the AlPO-n structure have been reported. At present, more than 50 different crystal structures of AlPO-n have been reported, which is comparable to that of aluminosilicate zeolites, making the aluminophosphates an important class of microporous crystals." ... 

Various types of zeolites referred to as Faujacite (NaY, NaX), Mordenite, ZSM-5 and ALPO-5 are aluminosilicate and aluminophosphate crystals consisting of mi-croporous cages of molecular dimensions (5-12 A) which are interconnected by smaller windows and channels, as is represented in Fig. 2. Such micropores can be used as ultimate nanometer-sized reaction vessels , providing a template for synthesizing nanomaterials such as selected metal clusters and nanoparticles which may fit the interior cages. Such bulky carbonyl clusters as Rh6(CO)i6 (van der Waals diameter of 10 A) and [Pti2(CO)24] (8 x 12 A) are unable to enter directly into the pores of NaY (12 A) through its smaller windows (6 A). 

Iron-substituted mesoporous aluminophosphate was used as a novel, efficient and ecofriendly catalyst for reductive cleavage of azo dyes and reduction in nitroarenes and catalytic transfer hydrogenation of nitro and carbonyl compounds. Unlike most of the iron-containing molecular sieves, dislodgement of tetrahedral Fe(III) was not observed upon various process treatments such... 

Many other catalyst systems have been investigated for toluene alkylation with the aim of reducing the loss in catalyst activity that results upon modification of the HZSM-5 zeolites with Mg, B, or P. The catalysts studied are aU acid and have the potential for molecular sieving to obtain high para selectivity. Examples include pillared clays [51], aluminophosphates [52], and carbon-exchanged NaY zeolites [53], as well as variously modified ZSM zeolites [5459] and nonzeolite molecular sieves [60]. Table 3 summarizes the results of some of these studies, from which it is concluded that no significant improvement in the performance of the catalyst reported by Kaeding et al. [49] has been made to date. An additional difficulty for this potential route to /i-xylene has been demonstrated by the comparative study of the performance of ZSM zeolites toward isomerization of w-xylene and toluene methylation [61]. For both reactions the activity was shown to decrease in the order ZSM-5 > ZSM-22 > ZSM-23, whereas... 

With the emergence of molecular sieves of new compositions, such as the aluminophosphate family, the structural complexity of the molecular sieve lattice has been greatly increased. For the reasons discussed above, the various NMR techniques are expected to play a dominant role leading to the understanding of these materials [14], complementing X-ray and other techniques in the characterization of the atomic order in the molecular sieve lattices. 

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