Characterization and catalytic properties of porous clay heterostructures from zirconium intercalated clay and its pillared derivatives

摘要

The insertion of zirconium or aluminium species into porous clay heterostructures has traditionally been performed in two steps. The first step prepares the porous clay heterostructures, and then adding the metal elements during the synthesis constitutes the second step. Here, a novel method is described that reduced the use of organic surfactants and inserted zirconium directly into the silica framework of the porous clay heterostructures in one step. It consisted of preparing the zirconium tetrameric species intercalated clay mineral as a precursor followed by co-intercalation of dodecylamine and the silica source (TEOS). The derived pillared zirconia clays were used as well as the precursor to prepare PCH materials. The materials were characterized by XRD, FTIR, TGA, Si-29 MAS NMR and XRF. The XRF technique confirmed the presence of Zr in the PCH material prepared from the intercalated clay. Improvements in specific surface area (918 m(2)/g) and pore volume (0.801 cc/g) were achieved. The concentration of Bronsted acid sites was deduced from the thermal desorption of cyclohexylamine and reached a value of 0.989 mmol of protons/g. This value was higher than the concentration for either the starting intercalated clay mineral or the derived pillared clays. Stronger Bronsted acid sites were developed into the PCH materials, in addition to Lewis sites, even at 500 degrees C, as indicated by the desorption of pyridine as a probe molecule. These acid sites were strong enough to convert n-heptane to isomers and cracking products. (C) 2016 Elsevier Inc. All rights reserved.