SILICALITE CHARACTERIZATION .1. STRUCTURE, ADSORPTIVE CAPACITY, AND IR SPECTROSCOPY OF THE FRAMEWORK AND HYDROXYL MODES

The physical properties (microcrystal morphology, crystallinity, internal perfection, adsorptive capacities toward CO and N2, and IR manifestations of the skeletal modes and of the hydroxyl groups) of a Na- and Al-free silicalite (S) prepared following a specifically designed method are investigated. Comparison is made with the silicalite containing Na and Al impurities prepared following a more conventional (classical) path (SNa). The experimental techniques are X-ray diffraction (XRD), high-resolution electron microscopy (HRTEM), infrared spectroscopy in reflectance mode (FTIR), and volumetric isotherms in a BET apparatus. The most relevant results are as follows: (i) S microcrystals have very regular octagonal prismatic habit, (ii) nanodefects and microcavites are more aboundant in S than in SNa, (iii) hydroxyl groups are present at the internal defects sites, and (iv) N2 and CO volumetric isotherms at 77 K differ from S and SNa.