Robust Pd/Al2O3 bifunctional catalyst for single reactor tandem synthesis of furan and tetrahydrofuran derivatives from furfural

In this study, we report a reusable catalytic system based on a bifunctional Pd/Al2O3 spheres to conduct the single-reactor tandem aldol condensation/crotonization reaction between furfural and methylisobutyl ketone, followed by hydrogenation, both in batch and continuous mode. In batch mode, the process achieved an overall 86 % yield of 1-(tetrahydrofuran-2-yl)-5-methylhexan-3-one at 180 °C after 9 h at (5.2 wt% furfural concentration). The reaction rate for the aldol condensation/crotonization step decreased at higher FF concentration, suggesting the inhibition of Lewis acid centers due to adsorbed FF as inferred from kinetic modeling. In continuous mode, the catalyst was operated in a dual-type fixed bed reactor and reached 55 % steady-state conversion and 60 % and 35 % selectivity to 1-(furan-2-yl)-5-methylhexan-3-one and (E)-1-(furan-2-yl)-5-methylhex-1-en-3-one, respectively, after 12 h operation at 170 °C and a weight-hourly space velocity of 0.50 h−1 at high furfural concentration (18 wt%). NH3/CO2 temperature-programmed desorption and FT-IR spectroscopy implemented with adsorbed pyridine, NH3 and CO2 were used to assess the nature, strength, density and stability of the acid and basic sites.