MeAPO

Thirteen stmctures of various compositions, as AlPO SAPO, MeAPO, and MeAPSO, are available from UOP. 

JDF-20 is not stable to calcination and converts to a mixture of AlP04-5 and tridymite at 500°C. The JDF-20 synthesis gel also produces the 12-MR AlP04-5 when heated at 200°C rather than at 180°C. This will limit the utility of JDF-20, however, this molecular sieve can be prepared in MeAPO compositions (where Me = Li, Mg, Mn, Ga, B, Si, Ti, and Sn) that may provide interesting redox properties. 

There is no systematic nomenclature developed for molecular sieve materials. The discoverer of a synthehc species based on a characteristic X-ray powder diffraction pattern and chemical composihon typicaUy assigns trivial symbols. The early syn-thehc materials discovered by Milton, Breck and coworkers at Uruon Carbide used the modem Lahn alphabet, for example, zeoHtes A, B, X, Y, L. The use of the Greek alphabet was inihated by Mobil and Union Carbide with the zeoHtes alpha, beta, omega. Many of the synthetic zeoHtes which have the structural topology of mineral zeoHte species were assigned the name of the mineral, for example, syn-thehc mordenite, chabazite, erionite and offretite.The molecular sieve Hterature is replete with acronyms ZSM-5, -11, ZK-4 (Mobil), EU-1, FU-1, NU-1 (ICI), LZ-210, AlPO, SAPO, MeAPO, etc. (Union Carbide, UOP) and ECR-1 (Exxon). The one pubHcaHon on nomenclature by lUPAC in 1979 is Hmited to the then-known zeoHte-type materials [3]. 

Late 1970s to early 1980s SAPO and MeAPO molecular sieves... 

Si, metal ions Mg, Co, Mn, Fe, as well as other elements, led to the silicoalumi-nophosphate family SAPO , the metalloaluminophosphate family MeAPO and other elements, the ElAPO family, where the added element is incorporated into the hypothetical AIPO4 framework... 

In the metal aluminophosphate (MeAPO) family the framework composition contains metal, aluminum and phosphorus [27]. The metal (Me) species include the divalent forms of Co, Fe, Mg, Mn and Zn and trivalent Fe. As in the case of SAPO, the MeAPOs exhibit both structural diversity and even more extensive composihonal variation. Seventeen microporous structures have been reported, 11 of these never before observed in zeoUtes. Structure types crystallized in the MeAPO family include framework topologies related to the zeolites, for example, -34 (CHA) and -35 (LEV), and to the AIPO4S, e.g., -5 and -11, as well as novel structures, e.g., -36 (O.Snm pore) and -39 (0.4nm pore). The MeAPOs represent the first demonstrated incorporation of divalent elements into microporous frameworks. 

The spectrum of adsorption pore sizes and pore volumes and the hydrophilic surface selectivity of the MeAPOs are similar to those described for the SAPOs. The observed catalytic properties vary from weakly to strongly acidic and are both metal- and structure-dependent. The thermal and hydrothermal stability of the MeAPO materials is somewhat less than that of the AIPO4 and SAPO molecular sieves. 

The MeAPSO family further extends the structural diversity and compositional variation found in the SAPO and MeAPO molecular sieves. These quaternary frameworks have Me, Al, P and Si as framework species [27]. The MeAPSO structure types include framework topologies observed in the binary AIPO4 and ternary (SAPO, MeAPO) compositional systems and the novel structure -46 with a 0.7 nm pore. The structure of -46 has been determined [34]. 

Synthetic forms AlPO-34, CoAPO-44, CoAPO-47, DAF-5, GaPO-34, Unde D, Unde R, LZ-218, MeAPO-47, MeAPSO-47, (Ni(deta)2)-UT-6, Phi, SAPO-34, SAPO-47, UiO-21, ZK-14, ZYT-6... 

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. 

The chemical analysis of the synthesized samples expresses in the framework composition, that is, (MeIAlyPz)02 provides the as-synthesized sample framework composition, which is shown in Table 3.7, indicating the presence of about 1% of Me in the synthesized aluminophosphate [29], From the x-ray powder diffractograms (Figure 3.14), it is noted that the crystallized products exhibit all the characteristic reflections of the MeAPO-5 molecular sieves [140] and a high crystallinity and degree of purity [29],... 

FIGURE 3.14 X-ray powder diffraction profile of (a) AlP04-5 and (b) a powder pattern representative of the MeAPO-synthesized samples. 

The MeAPO family described here marks the first demonstrated Incorporation of the divalent forms of cobalt (CoAPO), Iron (FAPO), magnesium (MAPO), manganese (MnAPO), or zinc (ZAPO) Into mlcroporous frameworks during synthesis. 

The synthesis of a MeAPO molecular sieve typically uses an aqueous reaction mixture formed by combining a dissolved form of the divalent metal, orthophosphor1c acid, a reactive alumina, and an amine or quaternary ammonium templatlng agent (R>. The metal Is typically Introduced as the acetate or sulfate salt, or as the metal oxide dissolved In dilute phosphoric acid. A synthesis mixture Is prepared In one of two ways ... 

There are 18 reported MeAPO structure-types (Table I). Eight of these are zeolite structure analogs (17, 20, 34, 35, 37, 43, 44, 47) which were subsequently observed In AlPO,-based materials. Seven structure-types were first Identified In the A1P0 (5, 11, 14, 16, 31), SAPO (41), or MeAPSO (46) families (14.15). The remaining structures (36, 39, 50) were first observed In the MeAPO family. The x-ray powder diffraction patterns characteristic of the structure-types 5, 11, 17, and 20 (6.16,17) and 14, 18, and 31 (7) have been previously published. The x-ray powder patterns... 

Table I. Typical Templates and Structure-Types for MeAPO Molecular Sieves...

MeAPO Species Structure Type Typical Template Pore Size (nm)... 

Tetraethyl ammonium (TEAOH). In A1P0, synthesis, TEA0H templates the structure-types 5 and 18. In SAP0 and in MeAPO synthesis, structures 5 and 34 are produced. Both 18 and 34 have pore systems controlled by 8-rings and both have comparable, large void volumes. The presence of the Me or Si in the gel composition... 

Qulnuclldlne (QUIN). The template qulnudldlne yields the structure-types 16 and 17 (ERI) In A1P0 synthesis and types 16, 17, and 35 (LEV) In SAPO and MeAPO synthesis. Typical synthesis gels for the preparation of MeAP0-16 and -35 are ... 

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