Superhydrophobic and superacid magnetic catalyst induced highly selective aldol condensation and alkylation for high-density biofuels

Aldol condensation and hydroxyalkylation/alkylation reactions are the most widely used C–C coupling strategies to synthesize high-density biofuels. But their in-situ generated water is unavoidable and can reduce the acidity of catalyst, thereby inhibiting catalytic activity or triggering side reactions. Herein, novel superhydrophobic and superacid magnetic catalyst Fe₃O₄@SiO₂@F-SO₃H is designed and synthesized through simple cladding and chemical grafting. This magnetic catalyst can withstand high temperature up to 215 °C and displays much better superhydrophobicity (contact angle of 155.3°) and lipophilicity (contact angle of 0°) than those of classical Amberlyst-15 and Nafion-212. Notably this catalyst exhibits excellent activity, selectivity and stability for both aldol condensation and hydroxyalkylation/alkylation reactions of lignocellulose derived cyclic ketones and furans. After hydrodeoxygenation, three high-density fuels with density of 0.825, 0.881 and 0.887 g/mL were achieved. This work illustrates an efficient and convenient strategy to achieve high-performance acidic catalyst for synthesizing high-density fuels.