Efficient valorization of biomass-derived furfural to fuel bio-additive over aluminum phosphate

Aluminum phosphates (APO-5s) were synthesized and evaluated as heterogeneous catalysts for the valorization of furfural to furfuryl acetals (FAs) and furfuryl alcohol ethers (FAEs). Weakly acidic APO-5 (Al/P = 1) exhibited excellent catalytic performance with 96 % FA yield in ethylene glycol, and analysis of the acetalization reaction supported that adsorption and acidic catalyst sites co-catalyzed the reaction. In addition, the catalyst was stable and reusable though with some deactivation after five recycles. Oppositely, more acidic APO-5 (Al/P = 1.5) catalyzed the one-pot synthesis of FAE with 55 % yield in 2-propanol with unchanged performance in three successive reactions after intermediate calcination. The reaction pathway for the direct hydrogenolysis of acetal into ether by catalytic transfer hydrogenation and etherification was promoted by the co-solvent 1,4-dioxane, possibly by hydrogen bonding. The study demonstrates a simple approach to design APO catalyst systems allowing very efficient and highly selective valorization of furfural to fuel bio-additives.