Mixed oxide pillared clays

Mixed oxide pillared clays are a new form of pillared clays. They can be obtained by a combined hydrolysis of metal salts La/Al, Al/Fe, Fe/Cr, Fe/Zr, Cr/Al. Another route is the synthesis of complexes containing different metal cations GaAli2-Keggin structures or binary oxides. These mixed pillared clays will have other, more specific catalytic and adsorption properties, while the size and charge of the pillaring species can be changed. The main drawback of these pillared materials is the characterization of the pillars. 

Barrault, J., Bouchoule, C., Echachoui, K., et al. (1998). Catalytic Wet Peroxide Oxidation (CWPO) of Phenol over Mixed (AlCu)-pillared Clays, Appl Catal B Environ, 15, pp. 269-274. 

Selectivity in the dehydration of olefins is improved with pillared clays. Clays with aluminum oxide or mixed aluminum and iron oxide pillars converted isopropyl alcohol to propylene with more than 90% selectivity.256 A small amount of isopropyl ether was formed. When zeolite Y is used, the two products are formed in roughly equal amounts. A tantalum-pillared montmorillonite converted 1-butanol to butenes at 500°C with 100% selectivity at 41% conversion.257 The product contained a 17 20 16 mixture of 1 -butene/c/s-2-butene/fra/ s-2-butene. No butyraldehyde or butyl ether was formed. A pillared clay has been used for the alkylation of benzene with 1-dodecene without formation of dialkylated products.258 The carbonylation of styrene proceeded in 100% yield (6.50).259... 

In catalysis, oxides with well defined acidic and basic properties are used in different forms that have found application in numerous catalytic applications in the gas-solid and liquid-solid heterogeneous catalysis [3, 46, 47], Among the most used oxide materials in catalysis, we And (i) bulk oxides (one component metal oxides) (ii) doped and moditied oxides (iii) supported metal oxides (dispersed active oxide component onto a support oxide component) (iv) bulk and supported binary metal oxides to quaternary metal oxides (mixed oxide compositions) (v) complex oxides (e.g., spinels, perovskites, hexa-aluminates, bulk and supported hydrotalcites, pillared clays, bulk and supported heteropolyacids, layered silicas, etc.). 

The TPD spectra show an increase of the acidity due to the intercalation of Zr, except when the "ex-situ polymerisation" process is run at pH 3.9. In this latter case, the clay calcined either at 400 or 600 C presents almost the same total acidity as the Na-montmorillonite, even if the Zr02 content of the clay is very high. Different hypothesis may explain the increase of acidity of the three other samples. This may be due either to the presence of the pillars, to the accessibility of the internal surface, or to the junction between the pillars and the silica layers. Without additional experiments the comparison of the acidity and acid strength of mixed oxides, studied by Shibata et al. (14) with this system supports the last hypothesis. 

Previous studies carried out with clay based catalysts pillared by Fe hydroxo complexes [13] or mixed (Al-Cu or Al-Fe) complexes, have shown that the mixed PILCs lead to the most promising results for organic compounds total oxidation in water, by using hydrogen peroxide as oxidant [14-16],... 

---