Reactivity and structure of nickel-exchanged Prayssac vermiculite

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Abstract
The reduction of both lattice Fe3+ and interlayer Ni2+ ions in Prayssac vermiculite is shown to be governed by the same diffusional process, with the removal of water during the reduction assumed to be the rate-determining step. The collapsed structure of the vacuum-activated samples accounts for the difficulty in eliminating water and agrees with the inhibiting effect observed during the reduction. The Fe3+→ Fe2+ transformation is shown to be a redox process. The very weak reactivity of Ni0 particles towards C2H4 hydrogenation agrees with the assumption that most of Ni0 are encaged as atoms in the ditrigonal cavities.