The fine silt (2–5 μm) coarse clay (0.1–2 μm) and fine clay (<0.1 μm) fractions of a Vertisol from South Italy were studied with X-ray diffraction. The most reactive fine clay (<0.1 μm) fraction was investigated in detail using a curve decomposition method analysis of X-ray diffraction diagrams, FTIR spectroscopy and chemical analysis. In the soil parent material, the fine clay fraction was dominated by low-charge smectites (beidellite and montmorillonite) whereas, high-charge beidellite was the dominant clay mineral in the fine clay from the upper soil horizons. This suggested that high-charge beidellite was produced through alteration of the preexisting low-charge smectites and was the stable clay phase in this soil environment, characterized by high pH (>8.0). After K-saturation and 25 wetting and drying cycles, the high-charge beidellite from the soil horizons lost expandability far more than the original low-charge smectites.

Layered double hydroxides (LDH's) interlayered with silicate anions were prepared by reaction of tetraethylorthosilicate (TEOS) with synthetic meixnerite-like precursors of the type [Mg1−xAlx(OH)2][OH−]x·zH2O, where (1 − x)/x ≈ 2, 3, or 4. TEOS hydrolysis at ambient temperature occurred readily in the galleries of the hydroxide precursors with (1 − x)/x ≈ 3 or 4, but a temperature of ∼100°C was required to achieve silicate intercalation for the LDH composition with (1 − x)/x ≈ 2. On the basis of the observed gallery heights (∼7.0−∼7.2 Å) and 29Si MAS NMR spectra that indicated the presence of Q2, Q3, and Q4SiO4 sites, the intercalated silicate anions, which are formed by condensation reactions of silanol groups and partial neutralization of SiOH groups with gallery hydroxide ions, are assigned short chain structures. Also, some O3SiOH groups become grafted to the LDH layers by condensation with MOH groups on the gallery surfaces. The LDH-silicates exhibited comparable non-microporous N2 BET surface areas in the range 59–85 m2/g, but they differed substantially in acid/base reactivities, as judged by their relative activities for the catalytic dehydration/disproportionation of 2-methyl-3-butyn-2-ol (MBOH). Under reaction conditions where the LDH structure is retained (150°C), all the silicate intercalates showed mainly basic reactivities for the disproportionation of MBOH to acetone and acetylene. However, all the LDH silicates were less reactive than the corresponding LDH carbonates. Conversion of the LDH silicates to metal oxides at 450°C introduced acidic activity for MBOH dehydration, whereas the metal oxides formed by LDH carbonate decomposition were exclusivity basic under analogous conditions.