Toward understanding of the role of Lewis acidity in aldol condensation of acetone and furfural using MOF and zeolite catalysts

• Some metal-organic frameworks (MOFs) are active catalysts in aldol condensation.
• Fe-BTC provides 10 times higher activity than Cu-BTC in aldol condensation of acetone and furfural.
• Lewis acidity of MOFs is not enabling aldol condensation of acetone and furfural.
• Brønsted acidity due to defects and rehydration catalyzes aldol condensation of acetone and furfural.

The aldol condensation of furfural and acetone allow producing higher value products from simple organic compounds resulting from biomass processing. In this paper, a number of metal organic framework (MOF) materials possessing Lewis acidity were investigated as catalysts in this reaction. Experiments were carried out under batch reaction conditions in Parr stirred autoclave at 100 °C during 0–4 h. The catalytic results indicated that the aldol condensation over MOFs took place with the participation of acidic rather than basic centers. The catalytic performance of these materials exhibited could not be explained by their reported Lewis acidity. Experiments with heat-activated and re-hydrated samples showed that Brønsted acid sites could also be present in MOFs as a consequence of interaction of metal cation with surrounding water molecules. As a consequence, the catalysts having such generated Brønsted acidity exhibited enhanced activity in the reaction.

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