Effects of Thermal Activation Conditions on Physicochemical Properties of Nanosheet-Derived Mg-Al Mixed Oxides

Mg-Al mixed oxides possess acid-base sites, and have been investigated as catalyst supports for methane conversion. Examples include Ni/Mg-Al oxide catalysts for steam reforming or dry reforming of methane. The catalysts may be synthesized by constant-pH coprecipitation of metal salts or impregnation of Mg-Al oxides with Ni precursors. Mg-Al double hydroxide nanosheets derived by delamination of Mg-Al layered double hydroxides (LDHs) offer the opportunity to obtain high-surface area supports to achieve high metal dispersion. In this presentation, we report the synthesis of high-surface-area Mg-Al mixed oxides by thermal treatment of Mg-Al LDHs bearing isethionate (HO(CH)₂SO₃^–, Ise). Exchange of interlayer carbonate in MgAl-LDHs bearing CO₃^2– (MgAl-CO₃) with Ise induces stacking disorder in the lamellar structure as reported in the literature, and allows facile delamination of the resultant material, MgAl-Ise, in water. Despite the highly disordered structure of Ise-containing materials, thermal activation of them in air yielded Mg-Al mixed oxides with low surface area and CO₂ adsorption capacity. In contrast, thermal activation of them in N₂ or N₂ followed by air led to marked increase in CO₂ adsorption capacity up to ≈800% relative to those obtained by calcination only in air. In addition, these mixed oxides exhibit higher surface area and CO₂ adsorption capacity than those obtained from the initial MgAl-CO₃. We report these new findings and provide the rational of the significant impact of thermal activation conditions on physicochemical properties of Mg-Al mixed oxides. In addition, we report our recent results demonstrating a further improvement in the porous properties of Mg-Al mixed oxides through tuning of the type of interlayer anions and thermal activation conditions.