Aldol condensation of furfural and acetone over Mg-Al layered double hydroxides and mixed oxides

Liquid phase aldol condensation of furfural and acetone catalyzed by solid base catalysts (Mg-Al hydrotalcites and Mg-Al mixed oxides) has been investigated as a method to valorize short chain ketones obtainable from biomass pyrolysis for the production of higher-molecular-weight products usable as fuel components. The Mg/Al molar ratios of the investigated catalysts was varied in the range from 2 to 4 and their catalytic activity was tested at different reaction temperatures (20-100 degrees C) using several activation methods. Mg Al hydrotalcites were used either after calcination as mixed oxides or after subsequent contact with liquid water or steam as rehydrated materials. Both furfural-acetone condensation products, i.e. C-8 and C-13, were the desired products of aldol condensation reaction. Higher reaction temperature facilitated the dehydration step and enhanced the catalyst selectivity to both dehydrated products (C-8 and C-13). The best results were achieved with calcined catalyst sample having Mg/Al molar ratio equal to 3 at 100 degrees C (> 95% furfural conversion and > 90% selectivity to the desired products). The selectivity to the main by-product, diacetone alcohol, did not exceed 5% in any experiment. The ex situ rehydration of the calcined samples resulted in catalysts with a significantly lower activity, except the catalyst with Mg/Al molar ratio equal to 2. On the other hand, in situ rehydration caused catalyst activity improvement only in the case of the sample with Mg/Al molar ratio 3. (C) 2013 Elsevier B.V. All rights reserved.