For SAPO

There is limited patent literature available on manufacturing techniques for aluminophosphates. Although many patents describe AlPO synthesis, most described examples are small-scale preparations. The fact that at least two catalytic applications have been commercialized for SAPO molecular sieves indicates that they have been scaled-up to large quantities [55, 56]. A large-scale preparation of SAPO-34 is described in a recent patent [57]. 

Table 15.3 Preparative conditions for SAPO-34 in Table 15.4. All samples were stirred during crystallization. DPA = di-n-propylamine.

Because of the variety of Si locations (isolated Si and Si islands) in SAPO molecular sieves, frequently no correlation exists between Si content and the number of acid sites [105]. However, for SAPO with low Si content. Si sites are usually isolated and there is one acid site per Si. In general, the framework charge and, thus, the maximum number of acid sites in a SAPO should be related to the value of framework (Al-P) [106]. This relationship is true of zeolites too, because (Al-P) is equal to A1 if there is no framework P. Based on this relationship, the... 

Table I. Framework Composition and Quantitative Analysis of Ammonia Desorption Experiments for SAPO Molecular Sieves...

In addition to the rates of olefin reactions, mass transfer also plays an important role in determining the extent of propylene conversion and the product distribution from SAPO molecular sieves. Restrictions on molecular movement may be severe in the SAPO catalysts, due to pore diameters (4.3 A for SAPO-34) and structure (one-dimensional pores in SAPO-5 and SAPO-11). The deactivation of SAPO-5 and SAPO-11 catalysts may be more directly related to mass transfer than the coking of SAPO-34. Synthesis of large or highly-branched products, having low diffusivities, inside the pores of SAPO-5 or SAPO-11 essentially block internal acid... 

Transition metals help not only to preserve the activity of existing acid sites, but also may give rise to additional acidity. For SAPO-11 it has been... 

For SAPO-11 type materials it was observed (29) that the as synthesized SYN (with di-n propylamine template) the calcined (CAL), hydrated (WAT) and cyclohexane (CYC) saturated samples exhibit different XRD patterns as shown in fig.5. As for other molecular sieves it was important to determine if silicon was incorporated into the AIPO4 framework or not and subsequently if basic or acidic properties were induced depending if Si " was substituting Al or P ", respectively. The X-ray diffraction pattern analysis allowed us to show that A1 and P atoms are strictly alternate and that the material crystallizes in the non centro symmetric Ima2 space group with a = 1.867 (2), b= 1.3373 (2) and c = 0.84220 (9) nm (33). The channels along c axis are elliptical and are occupied by the di-n propylamine molecules. Disordered domains were also evidenced presumably... 

In some of the AlP04-n molecular sieves discovered in 1982 [1], it is possible to substitute part of the P and Al framework elements with Si [2]. In the resulting SAPO-n materials, isolated Si atoms occupy P sites, while patches of Si atoms replace locally P as well as Al atoms [3,4]. The degree of Si substitution and the substitution mechanism depend on the topology of the framework and on the synthesis method [4,5]. While the synthesis method does not seem to be critical for the incorporation of traces of Si in SAPO-5 and SAPO-11, extensive Si incorporation in these structures can be achieved only by using very specific synthesis recipes [4,6]. Silicon-rich crystals of SAPO-5 and SAPO-11, e.g., can be prepared by using aluminium isopropoxide as a source of aluminium and specific templates, viz. dipropylamine for SAPO-11 and cyclohexylamine for SAPO-5 [4,6]. 

We have examined temperatured-programmed desorption (TPD) and thermogravimetric analysis (TGA) of isopropyiamine on a series of Si-, Co-, and Mg-substituted AIPO-5 samples. The TPD-TGA results on the substituted samples show ammonia and propene desorbing in a well-defined feature between 575 and 650K, a feature not observed on pure AIPO-5. The results suggest that TPD-TGA measurements of isopropyiamine may be useful in determining the framework concentrations and acid site densities for SAPO-5, CoAPO-5, and MAPO-5. 

In addition to demonstrating that discrete acid sites are formed upon substitution into the AIPO-5 framework, we made two other important observations. First, the calcination conditions used for preparing all of the materials was critical. This had been reported previously for CoAPO-5 [6], but we found that it was equally true for SAPO-5. Second, materials prepared with high concentrations of either Co+2 or Mg+2 tended to have many defects. These materials exhibited reasonable pore volumes as measured by 62 uptakes however, larger molecules were unable to enter the structure. 

The samples were synthesized under hydrothermal conditions with a tetraethylammonium hydroxide template. Each sample was characterized by x-ray diffraction and only peaks corresponding to the substituted AIPO-5 structures were observed. The concentrations of Co, Mg, and Si for each sample were determined by ICP and are reported in Table 1, along with the gel concentrations, as Me/(Me+AI+P). All samples were calcined in dry O2, since calcination conditions were found to greatly affect results. Calcining the CoAPO-5 and MAPO-5 samples in air essentially destroyed the samples. Even for SAPO-5, calcination in air decreased the number of acid sites measured by TPD-TGA by more than half and substantially decreased the pore volumes which were measured by O2 adsorption at 78K and 64 torr (P/Po=0.4), even though x-ray diffraction patterns remained excellent and exhibited no measureable changes in peak widths. While some of the pore volumes reported in Table 1 are actually higher than the theoretical value of 0.146 cm3/g, the conditions used for the measurements were the same as those used in previous... 

As was mentioned this scheme seems to be valid for HZSM-5 zeolites. In our opinion for SAPO-5 which exhibit weaker acidity than HZSM-5 this mechanism is stopped at the stage of ethoxy groups formation and further oligomerization does not take place. It is in good agreonent with the observed... 

The presence of only one peak for SAPO-37 near 665 K for pyridine or 500 K for NH3 is also in agreement with the infrared results of the pyridinium ions removal (figure 4a) showing a sharp pyridine desorption near 550 K. This... 

In agreement with these results, SAPO-37 was found to be much less active than HY zeolite for the cracking of n-hepane (Table 1). This reaction requests the presence of strong acid sites. Nevertheless, the activity for SAPO-37 is significantly higher than that for NaY. For the cracking of 2,2,4-trimethyl pentane, a reaction that can be performed with much weaker acid sites, SAPO-37 presents a reasonable initial activity (for t = 5 min), although quite lower than that observed for HY. 

A significant difference, however, is the C4/C3 ratio the product distribution for SAPO-37 is virtually symmetrical, as one would expected from a simple 3-scission mechanism, while Y zeolites usually give an asymmetrical distribution with a C4/C3 ratio greater than one. This means that side reactions occur at much lesser extent in SAPO-37 than in PrNaY. 

It is evident from the data of Table 1 that dependence of catalytic performance of SAPO-31 on reaction temperature has the same trends as for SAPO-11, but exhibiting better characteristics than its coimterpart at the same time. The latter state is illustrated by higher content of octane isomers in the products, higher content of methylheptanes in Cg fraction and lower concentration ratios of... 

Davis and coworkers [104] studied " Xe NMR of xenon adsorbed in several SAPOs, ALPOs, and Y zeolites. From a comparison of the xenon chemical shift extrapolated to zero pressure, these authors concluded that Xe atoms feel significantly smaller electrostatic fields and field gradients in the aluminophosphates compared to aluminosilicates. The extrapolated chemical shift decreased from 97 ppm in erionite to 60 ppm in Y zeolite and to 27 ppm in AIPO4-5, with the values for SAPOs being intermediate to Y zeolites and AlPOs as would be expected from the acidity trends. They concluded as well that SAPO-37 does not contain separate aluminophosphate and aluminosilicate islands. Dumont et al. [105] also carried out xenon NMR experiments in SAPO-37. From xenon sorption capacity and the decrease in the chemical shift, their conclusion was that the framework of calcined SAPO-37 is unstable when exposed to moist air. 

Figure 13 A simplified structure of SAPO-11 showing possible cation position. The sites are analogous for SAPO-5.

Table 6 shows the results for dehydration of methanol to olefins over MAPO-n (n=5, 11, 36), SAPO-11, and ZSM-5. The selectivity in Table 6 was calculated based on the carbon number. MAPO-5 and MAPO-11 form few hydrocarbons, and a large part of the product on these catalysts is dimethyl ether. On the other hand, hydrocarbons are the main products over SAPO-11 and ZSM-5 however, the product distribution is largely different for SAPO-11 and ZSM-5. The main product on SAPO-11 was aliphatic hydrocarbons with a carbon number higher than 5. In contrast to SAPO-11, the main product over ZSM-5 is lower paraffins and aromatics. These differences are also attributed to the low hydride transfer over SAPO-11 resulting from its mild acidity. 

In situ treatment in an XRD heating chamber in a flow of gas. Heating rate 16 K/min for SAPO-34 and 35 K/h for SAPO-35 and SAPO-37. The spectra are recorded at the indicated temperature. 

Figure 17 Effects of metal cations Ion-exchanged for SAPO-34 upon catalytic activity for NO reduction with C,H .

Figure 21 shows the XRD patterns of Pd-SAPO-5 before and after CH4 combustion at 1,073 K. All diffraction peaks were assigned to those for SAPO-5, and there were no diffraction peaks from a second phase, and there were no changes in the angle as well as... 

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