STUDIES ON SYNTHESIS, THERMAL STABILITIES AND ACID-BASE PROPERTIES OFHETEROPOLYANIONS PILLARED LAYERED DOUBLE HYDROXIDES

Layered Double Hydroxides (LDHs) pillared with heteropolyanions (POMs) SiW(11)M (H2O)O-39(6-), were synthesized by direct anion exchange rea ctions in aqueous solution, and were characterized by elemental analys is, XRD and IR spectra. The XRD patterns give the d(oo1) value of 1.47 nm. Differential thermal analysis (DTA) combined with XRD and IR stud ies of samples calcined at different temperatures indicates that the t hermal decomposition of the samples takes place in three steps: the el imination of water molecules from the interlayer space (less than 250 degrees C); the elimination of hydroxyl groups from the brucite-like l ayers (between 400 similar to 500 degrees C), then amorphous materials are obtained, which crystallize upon calcination at temperature highe r than 600 degrees C. The results from isopropanol conversion show tha t the pillared products are more catalytically active than that of the LDH procursor and the corresponding K+ salts of the POMs, and there e xists two kinds of active sites (acid and base sites) on the surface o f the samples.