Silico aluminophosphates

Other materials, closely related to zeoHtes, with zeo-type structures are silico-aluminophosphates (SAPOs) and aluminophosphates (ALPOs) [6]. 

Alumipophosphate molecular sieve membranes. In addition to zeolites, Haag Tsikoyiannis [1991] have also briefly described another type of molecular sieve membranes consisting of AIPO4 units whose aluminum or phosphorous constituent may be substituted by other elements such as silicon or metals. These membranes are made from aluminophosphates, silico-aluminophosphates, metalo-aluminophosphates or metalo-aluminophosphosilicates. Like zeolites, these materials have ordered pore structures that can discriminate molecules based on their molecular dimensions. Their separation and catalytic properties can also be tailored with similar techniques employed for zeolites. The procedures for calcining the membranes or separating them from non-porous subsuates are essentially the same as those described earlier for zeolites. 

The silico-aluminophosphate molecular sieves represent a new class of microporous solid acid catalyst. The framework of the aluminophosphate molecular sieves is formed by tetrahedral arrangements of equal numbers of AIO4 and PO4 tetrahedra, with AT+ and alternating. The framework of AiPO is neutral. However, the AIO4 or/and PO4 may be substituted... 

In situ NMR has been applied to understand the chemistry of acetone on the silico-aluminophosphate catalyst HSAPO-34. The results of this investigation are interpreted in the context of methanol-to-olefin chemistry on HSAPO-34. 

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. 

TEM studies indicate that the polygonal silico aluminophosphates appear to have hexagonal external morphology with average size of the synthesized crystals in the range of 50-75 nm. 

Kuhl and Schmitt [107] discussed the similarities between the phosphorus-containing zeolites ZK-21 and ZK-22 and the silico-aluminophosphate SAPO-42. The phosphorous chemical shifts in all three microporous systems clearly indicate that phosphorus is in framework tetrahedral sites in each and that some... 

In the present study, (silico)aluminophosphates, esp. ALPO-5 samples, have been tested for their capacity in the hydroxyalkylation of phenol with formaldehyde and with isobutanal, a small as well as a more bulky aldehyde. The condensation of phenol has also been compared to other aromatics. 

Silico)aluminophosphate-molecular sieves are interesting materials as catalysts for the condensation of phenoi with carbonyl compounds, presumably because of the low acidity and the spacious constraints, decreasing catalyst deactivation. Especially ALPO-5, having a very low acid strength, gives good yields in the reaction of phenol with formaldehyde towards dihydroxydiphenylmethanes. In case of the phenol/isobutanai reaction, mainly monosubstituted products are obtained shape selectivity seems to retard a second condensation step. Ortho-substitution prevails, possibly caused by a contribution of Lewis-acid catalysis. 

Metal-aluminophosphate (MeAPO-n) and Silico-aluminophosphate (SAPO)... 

MTBE methyl tertiary-butyl ether PO propylene oxide SAPO silico-aluminophosphate SBU secondary building unit SDA structure-directing agent TBAOH tetrabutylammonium hydroxide TBHP a -butyl hydroperoxide TBOT tetrabutyl orthotitanate TEA tetraethylammonium... 

Derouane, E.G., Maistriau, L., Dumont, N., B. Nagy, J. and Gabelica, Z. (1990) Progresses in synthesis and characterization of large and veiy large pore (silico)aluminophosphate molecular sieves SAPO-37, SAPO-40 and VPI-5/MCM-9 in ref. [56], pp. 3-6. 

Crystalline aluminophosphates, silico-aluminophosphates, and isomor-phously substituted aluminophosphates represent a new class of molecular sieves which are considered as potential catalysts and adsorbents [ill]. 

The most efficient catalysts in liquid-phase oxidation of organic compoimds were crystalline mked oxides [1]. They are ionic mixed oxides or mixed oxides containing oxides supported on oxides. In the latter case, the catalytic activity of the oxide support is increased by adding one or more metal components or is obtained by immobilization of metal oxides on inactive oxide support. Metal ions were isomorphously substituted in framework positions of molecular sieves, for example, zeolites, silicalites, silica, aluminosilicate, aluminophosphates, silico-aluminophosphates, and so on, via hydrothermal synthesis or postsynthesis modification. Among these many mixed oxides with crystalline microporous or mesoporous structure, perovskites were also used as catalysts in liquid-phase oxidation. 

Some of the available membrane separation processes can already be applied on an industrial scale. Hence, inorganic ceramic membranes (zeolites and their derivatives, e.g. silico aluminophosphates), organic polymer membranes and facilitated transport membranes, which rely on a carrier molecule with high CO2 affinity to achieve selective CO2 transport (such as metallic ions or liquid amines), have been used in separating CO2 from flue gas in post-combustion. As single-stage separation with these membranes is still difficult, new membrane materials are being developed [1]. Typically, the initial separation of carbon dioxide accounfs for 60-80% of the total cost of CO2 sequestration [24,25]. 

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