On the stability of mixed M2+/M3+ oxides Original Research Article

The stability of Mg(Al)O formed by calcination of Mg–Al-containing hydrotalcites has been studied under steam-rich conditions (H2O:N2=1:1) at 600–650 °C and 1 atm. It was found that the MgO structure as well as a high specific surface area are maintained after calcination at temperatures up to 800 °C. It has further been observed that the steam stability of Mg(Al)O towards sintering is improved after calcination of hydrotalcite at higher temperatures: calcination at 800 °C gave an improved stability of Mg(Al)O compared to calcination at 700 °C. Further, the stability towards sintering was influenced by the Mg/Al ratio of the hydrotalcite. Mg(Al)O materials formed from hydrotalcites with a Mg/Al ratio of 5 exhibit better long-term stabilisation characteristics compared to a Mg/Al ratio of 3 after calcination at 800 °C. A partial or full substitution of aluminum with gallium in the oxide did not improve the steam stability. Changing the hydrotalcite synthesis procedure from co-precipitation to the alkoxide route did not significantly alter the steam stability after calcination.