Aldol condensation of furfural and acetone over MgAl layered double hydroxides and mixed oxides

• Significant effect of reaction temperature on product distribution.
• Ex situ rehydration leads to catalyst having lower activity.
• Calcined hydrotalcites provide the best activity.
• Sensitivity of catalyst activity to rehydration procedure.

Liquid phase aldol condensation of furfural and acetone catalyzed by solid base catalysts (MgAl hydrotalcites and MgAl 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 °C) using several activation methods. MgAl 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. C8 and C13, were the desired products of aldol condensation reaction. Higher reaction temperature facilitated the dehydration step and enhanced the catalyst selectivity to both dehydrated products (C8 and C13). The best results were achieved with calcined catalyst sample having Mg/Al molar ratio equal to 3 at 100 °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.

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