Synthesis and characterization of PILCs with single and mixed oxide pillars prepared from two different bentonites. A comparative study

Different PILCs with single oxide pillars of Fe, Cr and Zr and mixed oxide pillars of these metals and Al have been prepared from two bentonites: a co mmercial bentonite from Fisher Scientific Company (F bentonite) and a natur al bentonite from Peru (P bentonite). Several Al/metal, OH/metal and metal/ clay ratios were used in order to investigate the effect on the chemical an d physical properties, specifically the thermal stability of the synthesize d pillared clays. The structure of the pillared materials has been studied by XRD, UV Diffuse Reflectance Spectroscopy (UV DRS) and detailed analysis of N-2 adsorption isotherms. The thermal stability, acidity and reducing be haviour of these products were determined by using, respectively, thermogra vimetric measurements (TGA), ammonia-TPD and TPR. Likewise, the methane ads orption capacity for different samples was evaluated. The resulting materia ls exhibited basal spacings in the range of 7-25 Angstrom, with high surfac e areas (213-331 m(2) g(-1)) and a high contribution of micropore area (bet ween 50 and 80%) over the total surface area. Pillared clays prepared from F bentonite generally showed larger basal spacings and surface areas than t hose from P bentonite. Except for PILCs with Cr in the pillar, whose struct ure collapsed below 400 degrees C, most of the PILCs materials with single oxide pillars were found to be thermally stable up to 500 degrees C. A rela tively strong interaction between metal and aluminium in the pillars was ob served. The surface acidity, methane adsorption and thermal stability were increased by incorporating aluminium into the single oxide pillars of Fe, C r and Zr. Likewise, it was observed that the pillar structure in PILCs with mixed oxide pillars was affected by the Al/metal ratio. Thus, the Keggin s tructure in samples with a higher Al/metal ratio seems to predominate, wher eas the pillar structure in materials with a lower Al/metal ratio is simila r to that of PILCs with single oxide pillars containing no aluminium. (C) 1 999 Elsevier Science B.V. All rights reserved.