Pyridine sepiolite

The broad line 2H NMR results, combined with the H and 29Si MAS-NMR results, confirm that acetone-d6 molecules are able to penetrate into the microporous channels of sepiolite, and cannot be removed by heating to only 60°C. This result is in agreement with a previous study that found, on the basis of BET surface area measurements, that molecules such water, ammonia, ethanol, benzene and pyridine were small enough to fit inside the microporous channels [10],... 

The acidity of the different sepiolite samples has been compared at 200flC of pretreatment temperature. In Tables III and IV, are given the values of the intensity of the I.R. bands, corresponding to pyridine adsorbed on Lewis si+tes (cations included) at 1450 cm"1, and on Bronsted sites calculated as "b" parameter, from the intensity of 1490 and 1450 cm"1 I.R. bands. 

Table III. Intensity of the I.R. bands of pyridine adsorbed on sepiolite derivatives, b parameter calculated from equation 1, with an estimated error of 0.02.

Figure 2. I.R. spectra of pyridine adsorbed on different sepiolite derivatives after degassing at 150°C and 10 Pa. a) Mg b) Na c) La d) protonic e) Al f) Cr sepiolites.

The hydrothermal stability of the SA1 sample has been compared with that of the original SMg in Figure 6. The X-Ray diffraction pattern of an A1 sepiolite before (a) and after (b) steaming at 700aC, 100% steam and a natural sepiolite (SMg) also steamed at 7000C (c). The results indicate that after this thermal treatment an important fraction of the aluminic sepiolite remains unalterated, while the natural sample is completely folded. The folding of the sepiolite is shown by the disappearance of the (1,10) reflexion at 7.2, 20, and the appearance of a new reflexion at 8.9, 20 (16). Moreover, the adsorption of pyridine shows the presence of a residual Bronsted acidity in the SA1 after the hydrothermal treatment which is approximately 30% of the untreated sample. 

Kuang WX, Facey GA, Detellier C, Casal B, Serratosa JM, Ruiz-Hitzky E (2003) Nano-structured hybrid materials formed by sequestration of pyridine molecules in the tunnels of sepiolite. Chem Mater 15 4956-4967... 

Other organic molecules such as pyridine also have access to the intracrystalline tunnels of sepiolite, as demonstrated clearly by Inagaki (72a), Kuang (72b), and Ruiz-Hitzky (69). The latter has recently reviewed the subject of accessibility and concluded that, for sepiolite, larger molecules (Fig. 13), such as methylene... 

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