Synthesis of new Sn-incorporated layered double hydroxides and their thermal evolution to mixed oxides

A new series of (MgAlSnIV)-Al-II-Sn-III hydrotalcite (HT)-like layered double hydroxides (LDHs) with Mg:Al:Sn = 3:1:0 to 3:0:1 were synthesized for the first time by a simple coprecipitation method at room temperature. The physicochemical properties of both as-synthesized and their thermally decomposed products were investigated in detail by various analytical and spectroscopic methods such as powder X-ray diffraction (PXRD), chemical analysis, scanning electron microscopy (SEM), FT-IR spectroscopy, Sn-119 and Al-27 MAS NMR, simultaneous TG/DTA, and N-2 adsorption-desorption experiments. A single phase corresponding to LDH could be obtained in the composition range Mg:Al:Sn = 3:1:0 to 3:0.7:0.3. Above this composition, in addition to LDH, the MgSn(OH)(6) phase also was formed. The Sn-119 NMR showed a broad signal in the range -525 to -660 ppm for Sn atoms existing in a distorted octahedral environment. Thermal calcination of MgAlSn-LDHs at 450 or 700 degrees C resulted in the formation of MgO-like solid solution, in which both Al3+ and Sn4+ were dissolved. The surface area and pore volume had decreased with increasing Sn content for both as synthesized and calcined samples. Calcination at 1100 degrees C yielded a mixture of well-crystallized phases corresponding to MgO, MgAl2O4, and Mg2SnO4 "inverse spinel".