Furfural Adsorption and Hydrogenation at the Oxide-Metal Interface: Evidence of the Support Influence on the Selectivity of Iridium-Based Catalysts

Here, tetrakis(hydroxymethyl)phosphonium chloride-protected colloidal iridium nanoparticles were deposited by sol-immobilisation on three different supports (CeO2, NiO and TiO2) and were investigated for the liquid-phase direct hydrogenation (H-2 atmosphere) and catalytic transfer hydrogenation - CTH (N-2 atmosphere) of furfural to study the effect of the H donor. The occurrence of strong-metal support interactions in 1 wt% Ir/CeO2 catalyst, as disclosed by XPS, was revealed to be responsible for the high activity observed in the direct hydrogenation (81% conversion after 6 h) and for the unusual selectivity to 2-methylfuran (70%) under CTH conditions. On the other hand, Ir/NiO showed peculiar selectivity to tetrahydrofurfuryl alcohol in both H-2 and N-2 atmospheres (71% and 70%, respectively). The density functional theory calculations further showed that the unique selectivity of Ir/NiO may be ascribed to the adsorption properties of furfural on the support, which activates a dual-site hydrogenation mechanism.