Tungsten-incorporated cage-type mesoporous silicate: W-KIT-5

Abstract

Tungsten-incorporated cage-like cubic three-dimensional mesoporous silicate, KIT-5, was successfully synthesized by one-step direct hydrothermal synthesis procedure employing Pluronic F127 triblock copolymer as the structure directing agent under acidic conditions. The resulting material, labeled as W-KIT-5, was characterized by XRD (SAXS and WAXS), N2 sorption, HR-TEM, DR-UV–Vis, 29Si MAS NMR, Raman spectroscopy, H2-TPR and NH3-TPD to better understand the morphology, textural properties and nature of tungsten coordination. With an increase in tungsten content, the surface area decreased from 964 (for Si/W=100) to 425m2/g (Si/W=10) and the corresponding total pore volumes decreased from 0.68 to 0.42cm3/g. Interestingly, narrow pore size distributions centered around approximately 9.1nm were observed for all W-KIT-5 samples. Depending on the loading, the incorporated tungsten is shown to exist in the KIT-5 framework as well as in the extraframework position by complementary analytical techniques. The W-KIT-5 samples are also shown to possess low to medium type acid strength.