On the effect of zeolite acid property and reaction pathway in Pd–catalyzed hydrogenation of furfural to cyclopentanone

Aqueous phase hydrogenative rearrangement of furfural (FAL) to cyclopentanone (CPO) via furfuryl alcohol (FOL) has been studied over Pd catalysts supported on H–ZSM–5 zeolites. Pd states, zeolite properties and reaction condition parameters were optimized, affording 98% selectivity and 120 h⁻¹ specific reaction rate over 2% Pd/H–ZSM–5(25) catalyst at 160 °C and 3 MPa H₂. For hydrogenation of FAL–to–FOL, the activity was related to the Si/Al ratio and acid property of zeolite supports. For hydrogenative rearrangement of FOL–to–CPO, pure H–ZSM–5 zeolite could catalyze single–step conversion with relatively low reaction rate, whereas the presence of Pd sites could achieve multi–step transformation with remarkably increased rate, highlighting Pd–zeolite acid sites synergy. Proton and furanylmethoxy–relevant intermediates were captured with spin trapping electron paramagnetic resonance experiments, and 4–hydroxy–2–cyclopentenone and 2–cyclopentenone were also identified as key intermediates in tandem reaction pathway to produce CPO.