Effect of ultrasound on the structural and textural properties of copper-impregnated cerium-modified zirconium-pillared bentonite

In this study, the synthesis of zirconium-pillared bentonite modified with cerium was performed via two different methods by the application of conventional and ultrasonic treatments during the intercalation stage. To synthesise copper-impregnated pillared clays by wet impregnation, cerium-modified zirconium-pillared clays were used as supportive materials after being calcined at 300 degrees C. Ultrasonic treatment significantly decreased the required processing time compared with the conventional treatment of the synthesised pillared bentonites. Chemical analysis confirmed the incorporation of Zr4+, Ce4+ and Cu2+ species into the pillared bentonites. X-ray diffraction (XRD) patterns of zirconium-and cerium/zirconium-pillared bentonites prepared by conventional treatment show that one large d-spacing above 3.5 nm corresponds to the mesoporous delaminated part, and another small d-spacing above 1.7 nm is indicative of the microporous pillared part. Zirconium-and cerium/zirconium-pillared bentonites prepared via ultrasonic treatment exhibited similar results, with the same high d-spacing but with a second low-intensity d-spacing above 1.9 nm. The delaminated structures of the pillared bentonites synthesised by both methods were conserved after copper impregnation. Nitrogen-adsorption isotherm analysis showed that the textural characteristics of products synthesised by ultrasonic treatment were comparable to those of products synthesised by conventional treatment. Fourier-transform infrared spectroscopy (FTIR) analyses showed the presence of Bronsted- and Lewis-acid sites, and zirconium-pillared clays synthesised by conventional treatment exhibited increased numbers of Bronsted- and Lewis-acid sites after cerium addition and copper impregnation. However, the products synthesised by ultrasonic treatment exhibited an increased number of Bronsted- and Lewis-acid sites after cerium addition, but a decreased number of acid sites after copper impregnation. (C) 2011 Elsevier B. V. All rights reserved.