SAPO-34 material

Crystalline microporous silicoaluminophosphates have been patented as SAPO-n (1) or MCM-n (2) materials. The SAPO materials crystallize from an aqueous medium in the presence of organic templates, the MCM materials from a biphasic medium, using similar templates. Most of the actually known MCM s and SAPO s are crystallographically different apart from SAPO-34, SAPO-44, SAPO-47 and MCM-2 which have the chabasite topology (2,2) The structure of other MCM materials is presently unknown. 

The SAPO materials seem likely to provide novel catalysts, especially as the emphasis of zeolite usage turns to chemical intermediates and fine chemical production, and processes using the B analog of ZSM-5 (borahte) and SAPO-34 have been commercialized. 

The local environments of T-atoms in SAPO materials were examined using solid-state NMR, a bulk probe, and XPS, a surface sensitive probe. T-a-tom 2 p binding energies in XPS were found to vary in a predictable fashion with changes in NMR chemical shifts. The comparison demonstrates that XPS is sensitive to variations in the second coordination sphere for T-atoms in SAPO molecular sieves. XPS was also found to give a reasonable, quantitative measure of superficial (surface) T-atom fractions thus providing information about elemental homogeneity by comparison to bulk chemical analysis. 

Bulk and Surface Compositions. The chemical compositions of the molecular sieves used in this study are given in Table I in terms of tetrahedral atom (T-atom) fractions, and are grouped according to structure type. The bulk compositions of AIPO4-5, AlPO -20 and VPI-5 show the ideal 1 1 ratio of A1 and P characteristic of aluminophosphate molecular sieves. The SAPO materials have frameworks consisting of Si, A1 and P T-atoms. 

Phosphorus. Previous P solid-state NMR studies of SAPO materials have detected only a single type of local environment for phosphorus T-atoms four aluminum second nearest neighbors as in a pure aluminophosphate (ALPO ) material (3,4). This environment is illustrated in Figure 1. The NMR chemical shifts from this environment t)q)ically range from -25 to -35 ppm. 

Aluminum. Previous Al NMR studies have demonstrated four possible local environments for Al in SAPO materials (3,4). These environments are illustrated in Figure 3, and may be classified as either phosphorous rich (i.e., ALPO -like) with a chemical shift ranging from 30 to 40 ppm, or silicon rich (i.e., zeolite-like) with a chemical shift greater than 48 ppm. Both types of environments are characteristic of a substitution mechanism involving silicon substitution for phosphorus. A fifth possibility for an Al environment involves two Si and two P second nearest neighbors. However, no such environment has yet been identified by NMR, either because the Al chemical shift is similar to that for the silicon- or phosporous-rich environments, or because materials with an appropriate level of Si to give rise to... 

Finally we note that catalytic propoties of the In/SAPO materials obtained via template induced reduction might be utilized in organic reactions with highly reactive substrates which require nonacidic or weak acidic catalysts. 

The synthesis and characterization of a mesoporous silicoalumino phosphate are given employing typical structure directing reagent viz. cetyltrimethyl ammonium bromide. The Si MAS NMR showed that silicon is found in coordination with 1, 2, 3 and 4 A1 ions through oxygen bridges. The sorption characteristics of this new mesoporous SAPO material are also presented. Keywords Silico aluminophosphate, Mesoporous, ordered molecular arrays, MAS NMR. 

Figure 1. XRD pattern of the uncalcined mesoporous SAPO materials a = S], b = S2, c = S3.

The catalytic properties of several SAPO materials have been inspected by several other authors, for transformations such as n-butane cracking HI, xylenes isomerization 12, propylene oligomerization and toluene methylation 13l. Most of them, and specifically SAPO-37, presented mild acid character, similar to the one revealed in this study. 

SAPO-37, as other SAPO materials, has acidic properties similar to some forms of Y zeolites. Nevertheless, the usual synthesis does not produce a material having the strong acid sites required for demanding reactions, namely n-heptane cracking. These sites are found in HY, SAPO-37 s isostructural analogue. 

ATO and AFO type structures. At present the industrial process of lube oil dewaxing (ChevronTexaco) is realized on bifunctional catalyst with acidic SAPO-11 (AEL) component. Few examples in the literature devoted to comparative study of AEL-, ATO- and AFO-SAPO materials in hydroisomerization reaction are based on a single specimen of each catalyst, sometimes not phase-pure and often prepared by exotic or undefined method. Recently the authors found a new method for selective and reproducible synthesis of SAPO-31 (ATO type structure) materials in the presence of di-n-pentylamine and showed hydroisomerization efficiency of catalysts based on these systems [3,4]. 

Besides the molar gel composition (what is an obvious factor of influence), a strong effect on phase purity of crystallization product and its crystallinity is attributed to the origin of the reagents used in synthesis of SAPO materials. We have found that DiPenA template is very selective in SAPO-31 formation for the case of both aluminum isopropoxide and Reheis F2000 alumina hydroxycarbonate as a source of alumina as well as for different kinds of silica sources. In Table 3 catalytic properties of SAPO-31 prepared with different reagents are presented. 

The essential importance during stage of impregnation of SAPO material with precious metal is an origin of the latter. Usually tetraammine complexes of Pd or Pt are used for that purpose. Tetraammine complexes have definite composition and their water solution have practically neutral pH value. For the case of palladium loading we have checked the influence of another form of palladium, namely palladium dichloride, water solution of which possesses slightly acidic reaction. Catalytic data are presented in Table 4. 

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