On the structural changes of a saponite intercalated with various polycations upon thermal treatments

A comparative study of the evolution of the structures of Al-, Cr-, Al/Cr-, Zr-, and Ti-intercalated saponites when heated under oxidant or inert atmo spheres to give the final pillared solids is presented. The study has been carried out mainly employing DTA-TGA-DTGA, X-ray diffraction and nitrogen a dsorption techniques. Significant differences are observed between the ther mal behavior of the precursors depending both on the nature of the metallic intercalating oligomers and on the thermal treatment atmosphere. Textural analyzes from nitrogen adsorption data at 77 K are also considered. These r esults indicate that all the intercalated clays show important modification s of their structural characteristics on heating at 300 or 500 degreesC, a fact which has been related to the pillar distribution and to the presence of organic moieties in some of the intercalating species. This behavior has to be taken into account in order to establish reliably the catalytic appl ications of these materials. (C) 2001 Elsevier Science B.V. All rights rese rved.