Al-pillared saponites

Table 5 gives the basal distances and the surface areas of Al-pillared saponites prepared at pH = 4.8 (process 1) and heated to SOO C at 36" /h, then to 750X at 90°/h and kept for 4 hours at this temperature. 

Al-pillared saponites exhibit significant surface areas (150 - 250 m. g ) at 750°C suggesting that a good interlayer pillar repartition is reached preventing the sintering at this temperature. 

Complementary results on thermal stabilities of Al-pillared saponites are presented elsewhere (22). 

The A1 content fixed by the pillared clay increases with the pH and with the Al/clay ratio. According to the preparation process, the whole amount of the pillaring Al-species is not always completely fixed in the interlayer space. For some samples, it may be suspected that another Al-species is precipitated to a greater or lesser extent on the layer surface. The best stability of Al-pillared saponite is obtained under the following experimental conditions clay concentration < 5 g.l Al/clay < 5 mmol.g and pH values between 4.8 and 6.0. A very carefull thermal treatment is required up to SOOX (36 /h heating rate) to transform the intercalated species into oxide pillars. At 750 C, the surface areas are about 150- 250 m. g and the basal spacings dpoi about 17.3 A. According to these values, Al-pillared saponites may be used as catalysts of 7-8 A pore space. 

Al-pillared clays thermally stable up to 750 C have been prepared from easily available starting materials a natural clay, namely the saponite, and a commercial aqueous solution of Chlorhydrol. 

Starting from a natural clay, the saponite, Al-pillared clays have been easily ... 

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. 

A comparative study of the textural properties developed by the intercalation and pillaring of a saponite with various aluminium oligomers is reported. Three aluminium polycations, [A1 304(P2-OH)24(H20)i2] ", [Al,3(P3-OH),(p2-OH),2(teM)6(H20)6] " and... 

The acidities of cliys and pillared clays are between those of amorphous aluminosilicates and zeolites. Pillared clays can provide large-pore two-dimensional networks. Hectorite, montmorillonite, saponite and beidellite are the clays most often used to make pillared clays. Most pillared clays coke and deactivate st. This, and low thermal and hydrothermal stabilities have so far limited catalytic applications. Al, Ti, Zr, Cr, Si, and Fe and their mixtures give more stable pillars than those tried in the past. Occelli and Robson reviewed pillrued clays [52]. 

Bergaoui, L. et al.. Porosity of synthetic saponites with variable layer charge pillared by A1j3 polycations, Langmuir, 11, 2849, 1995. 

Fig. 4 shows the 001 line evolution of sample la with regard to the thermal treatment. Pillared clays of process 1 (Table 5) still exhibit thermal stability at 750°C. These thermal stabilities up to 750°C may be related to (i) the nature of the phyllosilicate (magnesian octahedral sheet, Si/Al substitutions) and (ii) the thermal stabilization of the intercalated saponite. 

TABLE 5 Optimization of the Pillaring of a Saponite 45 Al-pillarcd saponilc characterization with regard to thermal treatment ... 

Recently, Takahama et al. (18) have reported that a montmorillonite expanded with SiOj TiOj sol particles (4), when dried with a supercritical fluid, can generate an expanded clay mineral with a surface area and pore volume more typical of silicas than of pillared clays (18,12). It is the purpose of this chapter to examine the physicochemical properties of two smectite (montmorillonite and saponite) samples expanded with Si02 Ti02 clusters and dried using a CO2 fluid at supercritical conditions. 

The air dried (400°C/2h) expanded saponite exhibits bands near 3738 cm , 3668 cm , and 3590 cm , attributed to silanol groups associated with the pillars, with structural OH, and with Si-OH-Al groups in the tetrahedral layers resulting from isomorphous substitution... 

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