Production of Furanic Fuel Precursors via Aldol Condensation of Bio-Derived Compounds Using Sn-Beta Zeolite Lewis Acid Catalysts

Furfural-acetone aldol condensation provides a promising route to oxygenated C8 and C13 precursors for aviation and diesel-range fuels. Here, we investigate tin (Sn)-modified beta zeolites as Lewis-acid catalysts, which have been prepared via post-synthetic incorporation of framework Sn(IV) while preserving the crystallinity and porosity of the Beta framework. This catalyst family was used to investigate structure-performance relationships linking zeolite topology, Lewis versus Brønsted acidity, Sn loading, and active-site accessibility on catalytic activity and stability. Among the investigated catalysts, 2Sn-Beta provided the best balance between activity and selectivity, achieving 76% furfural conversion with 50% selectivity to the C8 monomer, while 10% selectivity of C13 dimer was achieved at optimized conditions (145°C, 4 h). Lewis acid sites (LAS) are decisive for efficient C─C coupling, while Brønsted acidity provides limited activity. Reusability tests revealed a 30% decrease in furfural conversion after three consecutive runs, while C8 selectivity remained constant. Post-reaction characterization and regeneration experiments show that deactivation is mainly caused by reversible carbonaceous deposition and pore blocking rather than framework degradation or Sn loss, as catalytic activity was restored after calcination at 550°C. Overall, the study provides mechanistic insight into the interplay between acidity, accessibility, and catalyst stability in furfural upgrading over Sn-Beta zeolites.