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A new series of Mg II Al III Sn IV 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, 119 Sn and 27 Al 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 119 Sn 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 °C resulted in the formation of MgO-like solid solution, in which both Al 3+ and Sn 4+ were dissolved. The surface area and pore volume had decreased with increasing Sn content for both assynthesized and calcined samples. Calcination at 1100 °C yielded a mixture of wellcrystallized phases corresponding to MgO, MgAl 2 O 4 , and Mg 2 SnO 4 "inverse spinel".

Our recent study on the incorporation of Sn in the lattice of MgAl-layered double hydroxides (LDHs) indicated that about 30 atom % of Al3+ could be isomorphously substituted by Sn4+ to form a new MgAlSn ternary LDH. In the present study, similar NiAlSn- and CoAlSn-LDHs were synthesized by a coprecipitation method. The influence of Sn on the thermal transformation and redox properties of NiAl- and CoAl-LDHs and their thermally derived products were investigated by X-ray powder diffraction (XRD), thermogravimetry/differential thermal analyses (TG/DTA), and temperature-programmed reduction (TPR) methods. The thermal transformation and reducibility of NiAlSn-LDH were different from that of the CoAlSn-LDH. Sn crystallized out as a SnO2 phase along with NiO and NiAl2O4 phases from NiAlSn-LDH calcined above 900 °C. On the other hand, a mixture of nonstoichiometric Co-spinel and Co2SnO4 inverse spinel phases was noticed from CoAlSn-LDH. The TPR profiles of NiAl-LDH and its calcined products exhibited peaks for the reduction of Ni2+ species existing in different chemical environments while an additional peak for the reduction of Sn4+ → Sno was observed in the Sn-containing counterparts. The Sn incorporation greatly enhanced the reducibility of Ni-containing phases. The CoAl- and CoAlSn-LDH and their calcined products exhibited complex TPR profiles. At least three different reduction regions were identified. They were assigned to the reduction of Co2+−Co3+ (Co3O4-like) species (region I, between 250 and 450 °C), Co3O4-like species containing Al3+ or CoAl2O4-like species containing Co3+ (region II, 500−550 °C) and Co2+−Al3+ (CoAl2O4-like) species (region III, above 550 °C). In contrast to that observed in the Ni-containing analogues the reducibility of Co species in these samples was found to decrease upon Sn incorporation.

The amorphous aluminosilicate allophane was synthesized by rapid mixing of inorganic solutions with high initial concentrations (10 – 100 mmol/l) followed by hydrothermal treatment. X-ray diffraction (XRD) and transmission electron microscopy (TEM) revealed homogeneous products having a hollow spherical amorphous structure with a particle diameter of 3 – 5 nm. The amorphous products had a high BET specific surface area (490 – 552 m2/g) in comparison with natural allophane and had a narrow pore-size distribution (2 – 5 nm in diameter). The results of water vapour adsorption isotherm studies showed a gradual increase over the range of relative water vapour pressure of 0.6 – 0.9 and reached a maximum of ∼85 wt.%. The synthetic allophane shows promise as an adsorbent material because of its high adsorption-desorption capacity and its unique structure.