Vermiculite pillared

Hitherto the most successful pillaring has been carried out on smectite type clays. The original research on pillaring included several series of unsuccessful experiments on mica, vermiculite and the sheet silicic acid minerals magadiite, silhydrite and kenyaite. Recently renewed attention has focused on these and other alternative sheet structures. They include rectorite, zirconium phosphates, tetrasilicic micas, hydrotalcites and silicic acids, the general structural features of which are shown in Figure 4. 

Sepiolite is a fibrillar silicate which has been also used as a nanoclay in PLA, compared with both montmorillonite and halloysite. The use of pillared serpentines as support for ZnO catalyst for PLA polymerization has been recently reported. Zhang et al. obtained vermiculite/PLA nanocomposite by in situ polymerization of the PLA °. The use of different synthetic micas as nanofillers in PLA has also been evaluated. ... 

FIGURE 3 X-ray difraction patterns of Al-pillared vermiculite and phlogopite after... 

FIGURE 9 Relative variation of the normalized band areas of the Py-B (at 1545 em and Py-L (1448 cm ) bands versus outgassing temperature for Al-pillared vermiculite (V5) and Al-pillared phlogopite (P5). 

FIGURE 17 Variation of octane conversion (squares), yields of C8 isomers (triangles) and cracking products (circles) versus reaction temperature for Al-pillared vermiculite (filled symbols) and Al-pillared phlogopite (open symbols). 

K for Al-pillared vermiculite, for overall conversions of 85% and 88% and selectivities to C8 isomers of 94% and 91%, respectively. Under similar conditions, Al-pillared montmorillonite and saponite exhibited a maximum yield of isomers of 61.5% at 574 K and 70.4% at 524 K, respectively (100). The results obtained over the pillared vermiculite and phlogopite are the best ever obtained with Al-pillared materials and most of the commercial zeolites. 

FIGURE 8 Nitrogen adsorption-desorption isotherms at 77 K of (1) initial vermiculite (left) and phlogopite (right) after the conditioning treatment (2), and of the Al-pillared forms after calcination at 773 K (3) and 973 K (4). 

Recently, Quevedo et al. evaluated different solids as catalysts— a natural bentonite from Colombia, homogenized calcium bentonite, Al-pillared bentonite, a mixed oxide (Al203-Mg0, M3+/(M2++M +)=0.5), and an Al-Zr pillared vermiculite— in the Pictet-Spengler reaction between dopamine hydrobromide and aromatic aldehydes to synthe-tize the 1,2,3,4-tetrahydroisoquinoline [141]. The best yields, up to total conversion, were obtained when the mixed oxide was used as catalyst. It seems that this catalyst exhibited acid-base pairs due to the presence of sites... 

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