Reactivity and structure of nickel-exchanged Prayssac vermiculite

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.