Zr-exchanged and pillared beidellite: preparation and characterization by chemical analysis, XRD and Zr K EXAFS

Abstract

Zirconia-pillared clays (with synthetic beidellite as host material) were prepared by replacing the sodium interlayer cations by zirconium hydroxy polycations, and then heating to stabilize the structure. The pillaring solution was an aqueous zirconyl chloride solution. The process was first optimized in order to decrease the volume of solution and the reaction time. From the XRD results, the interlayer spacing was found to be near 9 Å in Zr-exchanged beidellite and slightly lower (7 Å) after calcination. The B.E.T. surface area equals 174 m² g⁻¹. In order to follow the pillaring process, an EXAFS study at the Zr K edge was carried out on crystalline zirconyl oxychloride, the pillaring solution, ion-exchanged and pillared beidellite. There is no difference between the nearest and next-nearest-neighbour environments of Zr in solid zirconyl oxychloride and the pillaring solution. Furthermore, it is found that the Zr environment of the zirconyl polycation is preserved in the pillaring process. Although the mean Zr–O and Zr–Zr distances are shortened from 2.21 and 3.59 Å, respectively, in exchanged beidellite to 2.17 and 3.38 Å, respectively, in the calcined material, the nearly square frame of the Zr₄ zirconyl units is also preserved after the calcination process. The results are consistent with the intercalation of zirconyl pillars made of isolated zirconyl polycations normal to the (001) planes of the beidellite layers. From the charge deduced from chemical analysis, one polycation cancels the charge of four unit cells of the beidellite.