Al-pillaring

Influence of Preparation Conditions on the Catalytic Properties of Al-Pillared Montmorillonites... 

Brindley and Sempels (1), Vaughan et al. (2) and Shabtai (3) have shown that the experimental conditions of Al intercalation influences the physicochemical properties of the clay. The nature, amount and spacial distribution of the pillars change the thermal stability, texture and acidity of the pillared clays. For example, Rausch and Bale (4) have reported that the OH/Al ratio modifies the structure of the Al complex and that monomeric [Al(0H)x(H20)6-x] " or polymeric [A1i304(0H)24(H20)i2] species can be obtained. Clearfield (5) demonstrated that the polymerisation state of Zr species depends on the temperature, concentration and pH of the solutions. In any case, the height of pillars is largely controlled by the polymerisation state of the intercalated complexes. However, in order to maintain the accessibility of the inner surface, the density or spacial distribution of the pillars has to be controlled. This parameter has been studied by Flee et al (5), and Shabtai et al (7) for Al pillared clays and Farfan-Torres et al (8) for zirconium. 

Fig. 7.17 Relation of the spinel structure (left) io the structure of sodium beta alumina (right). The sodium ions are free to move in the open spaces between spinel blocks, held apart by Al—O—Al pillars in the "parking garage structure. [In part from Wells. A. F. Structural Inorganic Chemistry, 5th ed. Oxford University Oxford, 1984. Reproduced with permission. ...

Fig. 80. 2,A1 (at 104.22 MHz) and 2 Si (at 79.8 MHz) MAS NMR spectra of (a) dried gel precursor used for synthesis (b) Na+-exchanged synthetic beidellite (c) Al3 + -exchanged variant of (b) (d) Al-pillared variant of (b). Peaks labeled SS are spinning sidebands. The precursor gel is seen to contain its silicon predominantly in the Si(4Si) environment (Q ), but some Si(3Si,OH) cannot be ruled out (462).

Figure 11.12. Nitrogen isotherms determined on (a) a montmorillonite, (b) the untreated La-Al-pillared montmorillonite, (c) after autoclaving treatment (after Sterte, 1991).

Aceman, S., N. Lahav, and S. Yariv. 2000. A thermo-XRD study of Al-pillared smectites differing in source of charge, obtained in dialyzed, non-dialyzed and washed systems. Appl. Clay Sci. 17 99-126. 

Nanosized sulfated tin oxide (STO) particles dispersed in the micropores of Al-pillared clay (STO/Al-P), were used by Mishra and co-workers [91] as an environmentally benign, recyclable and efficient catalyst for the solvent-free synthesis of 3,4-dihydropyrimidin-2(l//)-ones 42 using a domestic microwave oven. The protocol offers advantages in terms of simple experimentation, reusable catalyst, excellent yields, short reaction times, and preclusion of toxic solvents (Scheme 31). 

Sowmiya M, Sharma A, Parsodkar S et al (2007) Nanosized sulfated Sn02 dispersed in the micropores of Al-pillared clay as an efficient catalyst for the synthesis of some biologically important molecules. Appl Catal A Gen 333 272-280... 

At this point, the most promising types of pillared clays for use as cracking catalysts are the pillared rectorite developed by Jie et al. (3) and the large pore Ce/Al-pillared smectites developed by McCauley W. Further studies will have to be performed in order to determine the feasibility of these to types of materials for this application. 

The adsorption branches of the isotherms (figures 1 and 2), at high relative pressures P/P°>0.2, remain parallel to each other after the consecutive thermal treatments, which indicates that the mesoporosity of the materials is not modified, affecting the decrease in the adsorption of nitrogen at low relative pressure values and therefore in the microporous zone. In addition, the adsorption branches of the Al-pillared material (Al-Wy), are seen to display lower values which decrease more quickly with the thermal treatment. 

Table 1 shows the values for specific surface area, Sbet and volume of N2 adsorbed at P/P°=0.98, Vad, of the pillared samples and the raw material. All the pillared samples show a more developed porosity than the raw material (montmorillonite). The specific surface area and pore volume increase in all the pillared samples, but the increase is greater in the Al/La-pillared samples than in the Al-pillared sample. The increase in specific surface area was consistent with the expansion of the structure observed by XRD. The Al-Wy sample had a Sbet of 195 mVg while the AlLa-Wy-100 had a value of 349 m /g. 

Chiral (Salen)Mn complex Al pillared clay Encapsulation /... 

PZC/IEP of Al-Pillared Analytical Grade Montmorillonite from Fluka... 

Figure 13. Reaction pathway in the disproportionation of 1,2,4-trimethylbenzene using Al-pillared clays [79],...

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. 

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). 

First, cation-exchanged TSM (M -TSM) was prepared from the parent Na form using a metal nitrate solution by the common cation exchange method, followed by calcination at 200-500 ""C for 3 h (procedure of calc. 1). Al pillaring was then achieved in a mixture of acetone and water (Yamanaka and Brindley 1979). The calcined M" -TSM (1.2 g) was dispersed in a mixed solution of acetone and water (50 ml each) and stirred for 30 min then, 150 ml... 

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. 

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

M. De Pra, et al.. Pillar-structured microchannels for on-chip liquid chromatography evaluation of the permeability and separation performance. 

In 2004, Jiang, et al. studied the esterification of n-pentanol with benzoic add using Al-pillared clay (PILC) supported 5042" /Ti02 superacid catalyst (Fang et al., 2010), and find that it is known that the generation of super acid sites in the system of 5042 /MJDy solid superacid is necessarily promoted by the sulfur of the metal oxides, the more acid sites formed, the higher catalytic activity exhibited. Therefore, Al-PILC carrier can effectively enhance the catalytic activity. 

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