The activity of PdIr/C bimetallic catalysts for the furfural conversion in alcohol solvent via competitive reactions of hydrogenation and acetalization

The bimetallic PdIr/C catalysts with various Pd:Ir ratios and Pd-Ir structures were applied for furfural conversion in 2-propanol solvent under mild conditions (35 C-degrees, 6 bar H-2). Pd/C, Ir/C were also tested. The role of iridium addition is analyzed. The concurrent hydrogenation and acetalization were analyzed. The hydrogen activation of the catalysts was necessary, especially to activate iridium. PdIr/C catalysts gave higher selectivity to furfuryl alcohol (FA) than Pd/C. The surface presence/share of oxidized Ir strongly influenced the selectivity. PdIr/C with 15 or 26 mol% Ir were mostly alloyed-PdIr with surface enriched in Pd and gave FA selectivity (85%), much higher than for Pd/C. The highest TOF and FA selectivity were correlated with lowest H-2 sorption heat, weakest H-2 adsorption strength. PdIr/C containing 5 or 9 mol% Ir with the surface enriched in Ir presenting stronger H-2 adsorption strength, activated acetalization, and significantly suppressed FA formation. The exceptional >99% selectivity to furfural diisopropyl acetal (no formation of furfuryl alcohol) was obtained over monometallic Ir/C catalyst containing only oxidized IrOx on the surface.