Diffraction results microporous solids

The use of the latest experimental analysis and detection techniques including liquid/ solid NMR, XRD, electron diffraction, and in situ analysis is very necessary for the studies on the roles of the SDAs in the crystallization process of microporous materials, which could help us gain a better understanding of the formation mechanism of the pore systems and reveal the real correlation between guest molecules or ions and the resultant frameworks. 

The XRD patterns of zirconium sulfate pillared clays obtained after 90 hours of intercalation with different zirconium acetate concentrations using 0.5 as sulfate to Zr ratio and the same clay concentration as used earlier are presented in Fig. 5. The diffraction data show the appearance of two first order reflections. The first one is at 23.4 A for the lowest zirconium concentration and appears as a shoulder at the same distance for 0.05 mol/L concentration. The second reflection is observed at approximately 12.3 A for the lowest concentration and at 13.7 A for 0.1 mol/L zirconium acetate. The first one results from the intercalation of sulfated zirconium species. Those species are more voluminous than the non sulfated one which gives a distance spacing at only 19.6 A. The better intercalation of sulfated zirconium species at low Zr concentration is probably due to the slow progress of polycondensation reactions. This process reduces the number of different zirconium species and gives a better cristallinity of the solid. Table 2 summarizes the textural properties of samples prepared with different zirconium concentrations. The decrease of the surface area with the decrease of the Zr concentration is probably due to the increase of the sodium clay layers by comparison with the intercalated layers. The microporous volume increases when the Zr concentration decreases. The higher microporosity is due to the important basal distance of this sample. 

Basic zeolites were prepared by in situ formation of caesium oxide by calcination of the parent acetate loaded in an increasing amount up to 26 caesium atoms per unit cell. X-ray diffraction and BET studies are consistent with good crystallinity and site accessibility retainings. CO2 TPD results show homogeneous location of the basic species inside the pores with one caesium oxide per supercage. The results are fairly correlated with the initial rates of the Knoevenagel reaction of benzaldehyde and ethylcyanoacetate. These basic solids provide well-adapted selective microporous catalysts for condensation reaction. 

Zeolites form another class of materials useful for fundamental studies . As mentioned earlier, zeolites are microporous silica-aluminates with micropores of dimensions comparable to organic molecules. The materials are unique, because these micropores are determined by the three-dimensional crystallographic structure of the material and catalytic events occur at the interphase of zeolite micropore and zeolite lattice. As a result the catalytically active sites are well defined. Zeolites are used in practice in the acidic form or promoted with metal or sulfide particles. High Resolution Electron Microscopy, Neutron Diffraction and Solid State NMR are techniques that arc applied for structural characterization and to study the behaviour of chemisorbed molecules. 

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