Efficient Synthesis of Liquid Fuel Intermediates from Furfural and Levulinic Acid via Aldol Condensation over Hierarchical MFI Zeolite Catalyst

A water-tolerant, basic, and hierarchical MFI zeolite catalyst was synthesized and applied in the aldol condensation reaction between biomass-derived furfural and levulinic acid. The results showed that the addition of poly(diallyl dimethylammonium chloride) significantly affected the textural and acid-base properties of hierarchical zeolite, which subsequently influenced the catalytic performance of hierarchical zeolite. In the aqueous phase, potassium-modified, hierarchical MFI zeolite (K/H-MFI-n) was more active for aldol condensation between furfural and levulinic acid than the potassium-modified, conventional MFI zeolite (K/MFI). This was ascribed to higher basic sites density and improved diffusion limitation of K/H-MFI-n. A 70.6% yield of aldol condensation product was achieved with a complete conversion of furfural at 100 degrees C for 9 h by K/H-MFI-0.6. However, only 27.4% yield of aldol condensation product with 55.1% furfural conversion was obtained by K/MFI at the same condition. Two major isomeric aldol products, beta-furfurylidenelevulinic acid and delta-furfurylidenelevulinic acid (beta-FDLA and delta-FDLA), were obtained after acidification. K/H-MFI-n displayed an enhanced selectivity (54.9%) to delta-FDLA, owing to the stronger basicity of K/H-MFI-n. However, K/MFI showed a preferred selectivity to beta-FDLA (42.7%), owing to the dominant Lewis acidity. Recyclability research showed that the catalytic performance of potassium-modified, hierarchical MFI zeolite was acceptable after five runs.