Layer aluminosilicates catalyze reactions in numerous ways. They stabilize high-energy intermediates. They can store energy in their lattice structures and can release it in the form of chemical energy. They can catalyze redox reactions and can serve as photocatalytic devices. They often exhibit high surface acidity. Organic reactions that are catalyzed by the agency of days are reviewed. The role of clays in prebiotic chemistry is also examined.

https://science.sciencemag.org/content/sci/235/4795/1473.full.pdf

Chemical Reactions on Clays

The pulsed magnetic resonance technique was applied to the measurement of the longitudinal (T1) and transversal (T2) relaxation time of water molecules adsorbed by Na- and Ca-Montmorillonite, In the Na-clay the water was adsorbed as a monomolecular layer whilst in the Ca-clay, the bimolecular layer was formed under specified water vapor pressures. The effect of paramagnetic centers (Fe3+) was corrected and the samples were studied between + 30°C and −80°C. The main contribution to T1 was the “inter” contribution of protons diffusing from one water molecule to another whilst T2 results from simultaneous rotational (intramolecular) and diffusional (intermolecular) contributions. The proton diffusion coefficient and the life-time of a proton on one specified water molecule is derived from T1 inter. The calculated value at 298°C is equal to 10−7 times the life-time in liquid water, suggesting a dissociation degree 107 times higher in the adsorbed state than in liquid water. This increase in the dissociation degree as well as the reported activation energies are in good agreement with experimental data obtained from conductimetric and dielectric measurements performed previously.

Study of Water Layers Adsorbed on Na‐ and Ca‐Montmorillonite by the Pulsed Nuclear Magnetic Resonance Technique

Thermo-IR-spectroscopy analysis of the interactions between organic pollutants and clay minerals

Infrared spectroscopy has shown that two distinct types of copper (II) arene complexes can be formed by binding to dehydrated clay minerals.

Formation of Copper (II) Arene Complexes on the Interlamellar Surfaces of Montmorillonite

The acid-catalyzed reaction between methanol and isobutene to give methyl-t-butyl ether may be carried out using a cation-exchanged smectite as the catalyst. In 1,4-dioxan solvent at 60°C smectites exchanged with Al3+, Fe3+, or Cr3+ give yields of ∼60% after 4 hr, whereas smectites exchanged with Cu2+, Pb2+, Ni2+, Co2+, Ca2+, and Na+ give less than ∼8% yield. The reaction is efficient only when certain solvents are used, e.g., with Al3+-smectite the yield is ∼5% when using 1,2-dimethoxyethane, diethyleneglycol diethylether, n-pentane, tetrahydropyran, N-methylmorpholine, or tetrahydrofuran solvents compared with ∼60% using 1,4-dioxan solvent (4 hr). Moreover, the effective solvents depend somewhat on the clay interlayer cation. The use of tetrahydrofuran and tetrahydropyran gives ∼35% yields at 60°C (4 hr) with Fe3+- or Cr3+-smectites but ∼4% yield with Al3+-smectite.

SYNTHESIS OF METHYL-t-BUTYL ETHER FROM METHANOL AND ISOBUTENE USING A CLAY CATALYST

Des recherches recentes menees dans les laboratoires de Ducros, de Chaussidon et de Fripiat ont montre que l'eau residuelle fortement adsorbee par les surfaces internes de la mont-morillonite etait caracterisee par un degre de dissociation particulierement eleve. Il en decoule diverses consequences tant dans le domaine des proprietes physiques que chimiques. Le but de cette contribution est de montrer que des derives polycycliques adsorbes par la montmorillonite subissent de profondes modifications de structure. Le triphenylcarbinol forme l'ion triphenylcarbonium par reaction avec les ions hydrogene provenant de la decomposition de l'eau residuelle. Le coronene et l'ovalene adsorbes par les montmorillonites subissent des modifications dont la nature est encore hypothetique. La spectroscopic dans l'ultraviolet a ete la technique principalement utilisee mais la diffraction des rayons X a egalement fourni des indications interessantes .

Formation de radicaux libres sur la surface des montmorillonites

THE stability of crystalline cobalt (III) hexammine chloride up to 100° C and in solution is well known1. Morel2 has proposed the use of Co(NH3)3+6 for the determination of the cationic exchange capacity of clay. The fast colorimetric determination of an excess of reagent would provide an accurate routine analysis for cationic exchange capacity of clay minerals such as kaolinite and montmorillonite ; this method gives results in agreement with the classical ones, but with an alumino-silicate gel (cracking catalyst) steric hindrance precludes such an agreement.

Catalytic Decomposition of Cobalt (III) Hexammine Cations on the Surface of Montmorillonite

Protons de constitution, protons libres et eau adsorbée

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Formation de radicaux libres sur la surface des montmorillonites

Catalytic Decomposition of Cobalt (III) Hexammine Cations on the Surface of Montmorillonite

Protons de constitution, protons libres et eau adsorbée