A study of thermally activated Mg–Fe layered double hydroxides as potential environmental catalysts

Abstract

Layered double hydroxides (LDHs) and mixed oxides derived after thermal decomposition of LDHs with different Mg–Fe contents were investigated. These materials were chosen because of the possibility to tailor their various properties, such as ion-exchange capability, redox and acid–base and surface area. Layered double hydroxides, [Mg1-xFex(OH)2](CO3)x/2×mH2O (where x presents the content of trivalent ions, x = M(III)/(M(II) + M(III)) were synthesized using the low supersaturation precipitation method. The influence of different Mg/Fe ratios on the structure and surface properties of the LDH and derived mixed oxides was investigated in correlation to their catalytic properties in the chosen test reaction (Fischer–Tropsch synthesis). It was determined that the presence of active sites in the mixed oxides is influenced by the structural properties of the initial LDH and by the presence of additional Fe phases. Furthermore, a synthesis outside the optimal range for the synthesis of single phase LDHs leads to the formation of metastable, multiphase systems with specific characteristics and active sites.

Keywords

• Mg–Fe–LDHs
• hydrotalcite
• anionic clays
• Mg–Fe mixed oxides
• Fischer–Tropsch reaction