O

Figure 10.13. Configuration of sulphate group on the surface of a zirconia-suffate catalyst, showing the Lewis acid site Zr" at the left, and the Brensted acid site H+ at the right. [From G. Strukul et al., in Moser (1996), Chapter 6B, p. 147.]

Figure 10.13. Configuration of sulphate group on the surface of a zirconia-suffate catalyst, showing the Lewis acid site Zr" at the left, and the Brensted acid site H+ at the right. [From G. Strukul et al., in Moser (1996), Chapter 6B, p. 147.]

2,290

0 10 20 " 100 Zinconla in Zr02-Al2031 % Wt.

Figure 10.14. Cyanide group (-CN) infrared stretching frequency of CDsCM adsorbed on zirconia alumina catalysts as a function of zirconia (Zr02) content after evacuation at 25°C (upper curve) and 100°C (lower curve). The stretching frequency is a measure of the Lewis acid site strength. [From G. Centi et al„ in Moser (1996), Chapter 4, p. 81.]

2,290

0 10 20 " 100 Zinconla in Zr02-Al2031 % Wt.

Figure 10.14. Cyanide group (-CN) infrared stretching frequency of CDsCM adsorbed on zirconia alumina catalysts as a function of zirconia (Zr02) content after evacuation at 25°C (upper curve) and 100°C (lower curve). The stretching frequency is a measure of the Lewis acid site strength. [From G. Centi et al„ in Moser (1996), Chapter 4, p. 81.]

10.2.4. Pillared Clays

Clays ate layered minerals with spaces between the layers where they can adsorb water molecules or positive and negative ions, that is, cations and anions, and undergo exchange interactions of these ions with the outside. The clays that we will discuss (Clearfield 1996, Lerf 2000) can swell and thereby increase the space between their layers to accommodate the adsorbed water and ionic species. Figure 10.15b shows positive ions or cations between the layers, and Fig. 10.16 provides a more detailed sketch of an idealized clay structure with the prototype talc formula MgjS^OjoiOH^. The latter figure shows one and part of a second so-called silicate layer, and indicates the presence between them of exchangeable hydrated cations Mq+(H20)x, such as alkali or transition metal ions, with charge +q Mid n waters of hydration. In this idealized structure the four oxygen planes of the silicate

Figure 10.15. Saponite clay layers shown (a) before adsorption, (b) after adsorption of cations, and (c) after addition of pillars.

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