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Montmorillonites and other Mineral Adsorbents

AL-143
Mineral Adsorbents, Filter Agents and Drying Agents

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VI. MONTMORILLONITES AND OTHER MINERAL ADSORBENTS

An extensive series of catalysts has been prepared by the chemical processing of the mineral montmorillonite (Al2O3•4SiO2•xH20),3one of the major components of bentonite and Fuller’s earth.

Characterized by high catalytic activity, these products have shown the ability to promote reactions that usually require Brönsted or Lewis acid catalysis. Advantages include easy handling, chemical inertness (noncorrosiveness) and high economy.

A. Applications

In 1980, Professor Pierre Laszlo introduced a versatile catalyst for heterogeneous organic reactions termed clayfen [K 10/ Fe(NO3)3], consisting of iron(III) nitrate dispersed on K 10 clay.4 The catalyst is prepared5 by thorough mixing of an acetone solution of Fe(NO3)•9H2O with the clay followed by solvent removal on a rotary evaporator at 50°C. Note that, in a recent review,6 Laszlo points out that prolonged heating or bath temperatures > 50°C in the preparation of the catalyst can lead to an unstable reagent which decomposes in a vigorous exothermic reaction. Furthermore, clayfen should be used freshly prepared and never stored in closed containers.6

Applications of the catalysts include oxidation of alcohols4 and thiols,7 oxidative cleavage of thioacetals8 and N, N-dimethylhydrazones,9 conversion of hydrazines to azides,10 nitration,11 Diels-Alder catalysis,12,13 dehydration, esterifications, synthesis of enamines and selective halogenations.

 

Table 9
Catalog No. 281522 281530
Type K10 KSF
Surface Area (m2/g) 220-270 20-40
Pore volumea 0.318 at 0-80 0.023 at 0-80
Pore volumeb 0.29 at 15000-1750 0.19 at 15000-1750
  0.53 at 1750-80 0.05 at 1750-80
  0.13 at 80-14 0.04 at 80-14
  0.07 at 14-7.5 0.04 at 14-7.5
Loss on ignition (%) 7 7
Bulk density(g/l) 300-370 800-850

aml/g at nm range by CCI4
bml/g at nm range, Hg porosimeter