Synthesis and Dehydration Activity of Novel Lewis Acidic Ordered Mesoporous Silicate: Zr-KIT‑6

A zirconium-incorporated <i>Ia</i>3<i>d</i> cubic three-dimensional (3-D) mesoporous silicate, KIT-6, with different zirconium loadings, was synthesized via a one-step direct hydrothermal synthesis procedure employing Pluronic P123 triblock copolymer as the structure-directing agent under acidic conditions. Various characterization techniques, such as two-dimensional (2-D) small-angle X-ray scattering (SAXS), nitrogen sorption, temperature-programmed desorption of ammonia (NH₃-TPD), and ultraviolet–visible-light (UV-Vis) spectra, showed that zirconium was incorporated as Zr⁴⁺ ions in the KIT-6 framework, which retained the structural integrity with a highly ordered pore structure. The Zr-KIT-6 materials exhibit very high surface areas (810–980 m²/g) and large pore volumes (1.07–1.65 cm³/g) that decrease with an increase in zirconium content. In contrast, the pore size distribution remains relatively unaffected by zirconium loading with an average pore diameter of ∼9.3 nm. The Zr-KIT-6 materials possess Lewis acidity that increases with zirconium loading. In the 180–300 °C range, the Zr-KIT-6 materials are shown to be highly active for the test reaction of isopropanol (IPA) dehydration to propylene (selectivity >98%). The activation energy for IPA dehydration, estimated from intrinsic rate constants normalized with respect to the Lewis acid sites, was ∼49 ± 1 kJ/mol and found to be lower than most other Brønsted or Lewis acidic heterogeneous catalysts reported in the literature for IPA dehydration. Furthermore, these catalysts showed nearly stable activity with very little deactivation during extended runs at 260 and 300 °C