Silicoaluminophosphate crystal

In this study, we used the 29xe-NMR technique to examine the behavior of gaseous xenon adsorbed at different pressures on a series of intermediate phases isolated during the crystallization of a Faujasite-type silicoaluminophosphate, SAPO-37. Such a method has already proved successful in defining the different steps that successively occur during the crystaiiization process of zeoiites NaY, ZSM-5 and ZSM-20 [10] gel restructuration, increase of the crystallinity of the... 

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 entrapment-type nanocomposites can be prepared from zeolites and they are of two types zeolite-inorganic and zeolite-organic. Zeolite crystals are three-dimensionally linked network structures of aluminosilicate, aluminophosphate (ALPO), and silicoaluminophosphate (SAPO) composition and are porous, the pores being in the range of 2.8 to 10 A. Many of the highly siliceous, ALPO, and SAPO zeolites have been synthesized using organic templates such as tetrapropyl... 

The Si, Al, P composition is generally not homogeneous throughout the individual SAPO-n crystals [4]. SAPO-n crystals contain aluminosilicate domains (SA), where the silicon is concentrated, and silicoaluminophosphate (SAPO) domains. The Brpnsted acid sites of the SAPO-5 crystals of this work are located in the SAPO domains [21]. The SA domains do not contain aluminium and are catalytically inactive [21]. The Si(4Al) environment generates the Br0nsted acidity in SAPO-5. It represents 4% of the Si+A1 + P atoms in this particular sample [21]. In the SAPO-11 crystals used in this work, the Brqnsted acid sites are located in the SA crystal domains and at the interface of SA and SAPO domains [21]. Si(nAl) environments responsible for the Brpnsted acidity of SAPO-11 are not resolved from the 29 i resonance envelop (Fig.6). Their amount was estimated at ca. 1% of the Si+Al+P atoms [21]. 

Silicoaluminophosphates (SAPOs) are a new generation of crystalline microporous molecular sieves. They have been discovered by incorporating Si into the fr unework of the aluminophosphates (AIPO4) molecular sieves. Several small-pore SAPO crystals have been synthesized. SAPO-17, SAPO-34 and SAPO-44 have pore openings of about 0.43 nm. SAPO-17 has an erionite-like structure, while SAPO-34 and SAPO-44 have a chabazite-like structure. 

However, the incorporation of metal cations whose valence is different from that of A1 or P leads to the formation of electronically unsaturated sites, as schematically shown in Figure 3. This addition of aliovalent metal cations into the lattice of AlPO-n generates solid acidity and ion-exchange sites. There are numerous reports on the incorporation of many different metal cations into the lattice of AlPO-n. Table 2 summarizes the reported isomorphous substituted AlPO-n. The family of AlPO-n substituted with metal cations is generally called metal aluminophosphates (MeAPO-n). The typical metal cations substituted into AlPO-n are Li, B, Be, Mg, Ti, Mn, Fe, Co, Zn, Ga, Ge, Si, and As. The Si-substituted AlPO-n is called a silicoaluminophosphate and denoted as SAPO-n, where n also means the framework structure, and it is distinct from the MeAPO-n materials.SAPO-n exhibits both structural diversity and compositional variation. In particular, the crystal structure of SAPO-n is of greatest interest, because the distribution of the Si atom in the framework is quite complicated. Some crystal structures, such as SAPO-40, are only found in SAPO-n and not in AlPO-n or zeolite. The mole... 

Using N,N,N, N -tetramethyl-l,6-hexandiammine as organic template, SAPO-56 and its metal-containing silicoaluminophosphates (M=Co, Mn and Zr) were synthesized hydro-thermally. The synthesis phase diagram and crystallization kinetics of SAPO-56 were obtained. The synthesis regulation of pure MAPSO-56 molecular sieves was also investigated. The samples were characterized by XRD, SEM, TG-DTA and MAS NMR. SAPO-56 and MAPSO-56 were studied with respect to their catalytic behaviors in the methanol-to-olefms conversion and the oxidation of alkane, respectively. 

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. 

Recently, Yu and coworkers have successfully controlled the crystal size and morphology of the silicoaluminophosphate zeolite SAPO-34 (CHA) under microwave irradiation in the system of AljOj-P Oj-SiOj-TBAOH-H O by studying the synthetic factors such as the silica source, water content, crystallization time, and aging time [52]. Microwave-assisted synthesis proved to be an efficient approach to produce nanosized zeolite crystals [53]. As a comparison to traditional hydrothermal synthesis at 200°C for 72 h, the microwave-assisted synthesis of SAPO-34 needed only 1 h at 200°C, which greatly reduced the reaction time. 

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