Alkali-Free Zn-Al Layered Double Hydroxide Catalysts For Triglyceride Transesterification

Zn-Al layered double hydroxides (LDHs) of general formula [Zn(1-x)2+Alx3+(OH)(2)](x+)(CO32-)(x/2)center dot yH(2)O are promising solid base catalysts for the transesterification of lipids to biofuels. However, conventional synthetic routes employ alkali hydroxide/carbonate precipitants which may contaminate the final LDH catalyst and biofuel. The use of (NH3)(2)CO3 and NH3OH as precipitants affords alkali-free Zn-Al-LDHs spanning a wide composition range. The hydrothermal reconstruction of calcined Zn-Al-LDHs offers superior solid basicity and catalytic activity for the transesterification of C-4-C-18 triglycerides with methanol, compared with cold liquid phase or vapour phase reconstruction. Hydrothermally activated Zn-3.3-Al-LDH was stable towards leaching during transesterification.