Synthesis of Solid Acid Catalysts of MgO–Al2O3 Mixed Oxide Containing Oxyanions by Thermal Decomposition of Anion-Exchanged Hydrotalcites

Solid acid catalysts of MgO–Al₂O₃ mixed oxides containing B₄O₇²⁻, HPO₄²⁻, Mo₇O₂₄⁶⁻, MoO₄²⁻, WO₄²⁻, and SO₄²⁻ were synthesized by anion exchange with Cl⁻ located in the space between anionic layers of hydrotalcite, followed by heat treatment at 773 K. The distance between the hydroxide layers was expanded by the intercalation of oxyanions larger than Cl⁻. The exchange of oxyanions in the interlayer space was confirmed by IR spectroscopy. Acid sites were generated on the obtained mixed oxides of MgO–Al₂O₃ by the electron withdrawing effect of the oxyanions. The acid catalyzed ethanol dehydration into ethylene and diethyl ether took place on the obtained catalysts. The effect of exchanged anions in the generation of acid sites was the largest in SO₄²⁻.