MODIFICATION OF THE SURFACE-PROPERTIES OF NATURAL PHYLLOSILICATE SEPIOLITE BY SECONDARY ISOMORPHIC SUBSTITUTION

The alumination of sepiolite led to a material with a moderate Lewis a cidity, a high surface area, a microporous character, and a cation exc hange capacity (CEC). The CEC increased to 45 meq/100 g and extraframe work aluminum was formed. Alumination was accompanied by an increase i n the sodium content of the sample and an improvement of the thermal s tability, reflected in a microporosity more stable at 400 degrees C th an in the starting material. The CEC resulting from alumination allowe d for the dispersion of vanadyl cations without loss of crystallinity. Electron paramagnetic resonance spectra indicated an isolated, immobi le octahedral environment compatible with charge balancing vanadyl cat ions and/or vanadyl species at the edges of the octahedral ribbons in the framework. Upon alumination, the activity for ethanol dehydration was increased threefold at 400 degrees C to 85% with a selectivity for ethylene of 50%. Upon dispersion of vanadyl cations, the reactivity f or ethanol conversion was further increased. The possibility to apply successfully secondary isomorphic substitution techniques to natural m inerals was clearly established and it was shown to alter their surfac e properties considerably, as shown here on sepiolite from both spectr oscopic and reactivity studies. (C) 1995 Academic Press, Inc.