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 doub le hydroxides (LDHs) with Mg:Al:Sn = 3:1:0 to 3:0:1 were synthesized for th e first time by a simple coprecipitation method at room temperature. The ph ysicochemical properties of both as-synthesized and their thermally decompo sed products were investigated in detail by various analytical and spectros copic methods such as powder X-ray diffraction (PXRD), chemical analysis, s canning electron microscopy (SEM), FT-IR spectroscopy, Sn-119 and Al-27 MAS NMR, simultaneous TG/DTA, and N-2 adsorption-desorption experiments. A sin gle phase corresponding to LDH could be obtained in the composition range M g:Al:Sn = 3:1:0 to 3:0.7:0.3. Above this composition, in addition to LDH, t he 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 octahedr al 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+ an d Sn4+ were dissolved. The surface area and pore volume had decreased with increasing Sn content for both as synthesized and calcined samples. Calcina tion at 1100 degrees C yielded a mixture of well-crystallized phases corres ponding to MgO, MgAl2O4, and Mg2SnO4 "inverse spinel".