Entrained sodium in mixed metal oxide catalysts derived from layered double hydroxides

Abstract

The layered double hydroxide Mg6Al2(CO3)(OH)16·4H2O has been prepared using aqueous sodium hydroxide and sodium carbonate. Samples have been washed to varying degrees and then calcined to form the mixed oxides. Entrained sodium concentrations have been measured in all samples and compared with catalytic activities in a base-catalysed transesterification reaction, and with CO2 adsorption calorimetric data. The same materials have been prepared using routes not involving alkali metal compounds and compared in the same way. The results show that entrained sodium in these materials is difficult to remove, that it is associated with increased basicity and catalytic activity, and that, when incorporated at levels as high as 2% w/w, significant leaching can occur into reaction mixture. It seems likely that the sodium is entrained in the layered double hydroxide as sodium nitrate.