Zeolite Type A

The NO spectrum has now been studied for the molecule adsorbed on ZnO, ZnS (18), 7-AI2O3, silica-alumina, silica-magnesia (20), an A-type zeolite (97), H-mordenite (98), and a variety of Y-type zeolites including NaY (19), MgY, CaY, BaY, SrY (81), decationated-Y (19), ScY, LaY, and A1HY (99). The nitric oxide molecule has mainly been used as a... 

The unique properhes of zeolite materials combined with the conhnuous separahon properhes of membranes make zeolite membranes very attrachve for a wide range of separahon and catalysis applications. Zeolite membranes, however, have poor processability, poor mechanical stability and are much more expensive than the commercial polymer membranes with current state-of-the-art membrane manufacturing process. So far, the only large-scale commercial zeolite membrane is the A-type zeolite membrane and it has been used for dehydrahon of alcohols [22]. Further advancement in making thinner zeolite membranes and continuous improvement in membrane produchon techniques and reproducibility will make zeolite membranes more successful in commercial applicahons. 

Zeolites have attracted much attention as cobalt catalyst supports ]151-155]. Co2(CO)8 reacts rapidly from the vapor phase with X and Y faujasite type zeolites Co4(CO)i2, subcarbonyl species and [Co(CO)4] species form inside the pores. Further migration of Co4(CO)i2 carbonyl is inhibited because of pore size hmita-tions, and subsequent decarbonylation can take place only above 150 °C. In contrast, the reaction of Co2(CO)g with an A-type zeolite is limited to the surface due to the inability of the carbonyl precursors to pass through the apertures of the cavities of the structure. 

Tn recent experimental work in this laboratory (1-3) we have studied the kinetics and equilibria of sorption of light hydrocarbons and some other simple non-polar molecules, in 5A zeolite. The crystal structure of the A-type zeolites is among the simplest of the zeolitic lattices (4). In this paper we show that many features of the sorption kinetics and equilibria may be explained by simple theoretical considerations. 

The cavity of the A-type zeolite is approximately spherical with diameter 11.4 A. If the occluded molecule is regarded as a hard sphere, the free diameter of the cavity (the distance through which the center of the occluded molecule can move) will be reduced by a distance a corresponding to the van der Waals diameter of the molecule. The free volume of the cavity, and hence the value of K0 may be estimated on this basis. This method of calculation is equally applicable to other zeolites which consist of discrete cavities interconnected through small (eight-membered) oxygen windows. 

Attempts have recently been made to prepare solid acids by loading triflic acid into various inert oxides including silica,184 titania,185,186 and zirconia.187,188 Silica functionalized with anchored aminopropyl groups was also used to immobilize triflic acid.189 These new catalysts have been tested in a variety of organic transformations, such as alkane-alkene alkylation, Friedel-Crafts acylation, alkene dimerization, and acetalization. Silica nanoboxes prepared by dealumination of Na-X- and Ca-A-type zeolites were also loaded with triflic acid up to 32 wt%.190 The materials were thoroughly characterized but have not been tested as catalysts. 

A-type zeolite pervaporation membranes have been developed by Mitsui Engineering Shipbuilding Co Ltd, which have been implemented in an industrial... 

Possible pathways for the formation of faujasite and A-type zeolites from SiO and AlO tetrahedra. 

In this work we describe an extension of our previous work (18) to the synthesis of A-type zeolites over the range of composition 1.0 < Sl/Al < 3.0 and report the results of 2 Si NMR measurements made on these materials. We compare the data with those for faujaslte over the same composition range and discuss the nature of the SI and Al distributions In these materials. 

Finally, the structure composed of clusters of the fourth type, [Al3SiAlSi3] , has Si/Al = 1. Therefore, the H forms of A-type zeolites would contain only OH-IV groups. This is, however, only a hypothesis, since the H forms of A zeolites are unstable. 

Anderson and Imai (2) have studied -elimination involving a different leaving group, acetate anion. Both n- and 5 c-butyl acetates decomposed cleanly over faujasite, mordenite, and A-type zeolites to form mixed linear butenes as shown. Poisoning with product acetic acid occurred in some cases. 

S. Yamazaki and K. Tsutsumi, Synthesis of an A-type zeolite membrane on silicon oxide film-silicon, quartz plate and quartz fiber filter, Microporous Materials 4 205 (1995). 

Yamazaki S and Tsutsumi K. Synthesis of A-type zeolite membrane using a plate heater and its formation mechanism. Micropor Mesopor Mater 2000 37 67-80. 

Huang AS, Lin YS, and Yang WS. Synthesis and properties of A-type zeolite membranes by secondary growth method with vacuum seeding. J Membr Sci 2004 245 41-51. 

C. P. Herrero, /. Phys. Chem., 97, 3338 (1993). Monte Carlo Simulation of the Si, A1 Distribution in A-Type Zeolites. 

Quantum chemical calculations on cationic positions and adsorption complexes in A-type zeolite... 

In hydrocarbon processing the A-type zeolites are frequently used as adsorbents for purifying feeds and separating products but never as catalysts due to some inappropriate characteristics (e.g. stability and pore aperture). However, the simplicity of its structure and its well characterized ion-exchange properties make zeolite A suitable to models for investigating the redistribution of cations after various treatments and for studying adsorbent-adsorbate interactions (which finally may lead to chemical transformations). 

With small particles of Co encapsulated in A type zeolite and obtained by Cd metal vapor reduction of Co, a selectivity for propylene from syn-gas as high as 100 % was recently observed Frenkel, D., and Gates, B.C., J. Amer. Chem. Soc., 102, 2478 (1980). 

Although it is assumed in ref. (12) that the selectivity for propylene is due to the shape-selective A-type zeolite, we believe that selectivity is mainly due to particle size effect since non porous aluminas with small particles of Fe(15 A) leads also to high selectivity see also ref. (3e). The higher selectivity observed in ref. (12) with Co-clus-... 

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