Specific insights on the synergistic role of metal and acid sites of low loading Pd(PVA)/zeolite catalysts for furfural hydrogenation

The synergistic role of metal and acid sites in Pd colloids with polyvinyl alcohol (PVA) supported on zeolite catalysts was proved in furfural hydrogenation. Pd nanoparticles were prepared using PVA sol-immobilization and deposited on zeolites with different pore size (Y, ZSM-5 and FER) and similar Si/Al ratio to correlate the amount of accessible Brønsted and Lewis acid sites with catalytic activity and selectivity. Catalytic tests at 50 °C showed that Pd/Y is the most active catalyst, achieving 95.0 % conversion after 120 min. The presence of Pd is essential for furfural conversion, with bare zeolites showing minimal activity under the same conditions. Product distribution varies with the type of zeolite, with Pd/Y producing a complex mix including tetrahydrofurfuryl alcohol (THFA) and isopropyl levulinate ester (ILE) as the main product after 120 min, while other catalysts mainly form furfuryl isopropyl ether (FIE). FESEM-EDS, TEM, XPS and FT-IR measurements revealed that the most marked difference between Pd/Y and the other catalysts is the much higher amount of Lewis acid sites. This means that the synergistic effect between Pd and Lewis acidity is the key factor for obtaining THFA and ILE through H2 splitting and double bond activation.