Chromium-saponite clay catalysts:: Preparation, characterization and catalytic performance in propene oxidation

Chromium-saponite catalysts have been prepared by two synthesis procedures. The first method consisted in the intercalation of the saponite with solutions containing aluminium and chromium oligomers with various molar ratios, while the second one consisted in the incipient wetness impregnation of alumina-pillared saponite with several chromium salts, ammonium chromate, Cr(II) acetate and Cr(III) nitrate. Several techniques, X-ray diffraction, nitrogen physisorption at -196 degrees C, thermogravimetric and differential thermal analysis, infrared and DR-UV-vis spectroscopies, temperature-programmed reduction and electron paramagnetic resonance spectroscopy at - 196 degrees C, have been used to characterize and to compare the properties of the materials synthesized. The results show that the solids obtained combine the layered structure of the clay and the thermal stability given by the alumina pillars. The catalysts have been tested in the oxidation of propene, showing a catalytic behaviour according to the Mars-van Krevelen mechanism, the performance not depending on the method in which chromium was incorporated to the clay. (c) 2007 Elsevier B.V. All rights reserved.