Selective and sustainable quinoline hydrogenation with a robust hierarchical catalyst framework†

A hierarchical heterogeneous palladium on nickel foam-based catalyst system (Al₂O₃–Pd–D/Ni) was demonstrated for the selective hydrogenation of quinoline and quinoline derivatives under low H₂ pressures, with green solvents (ethanol, ethanol water mixture). The catalyst framework features very low palladium loadings and is highly reusable under facile handling, requiring no filtration or other separation aids, and notably demonstrates no loss in reactivity or alteration of selectivity over multiple recycling trials. Theoretical calculations and X-ray photoelectron spectroscopy studies point to a fully-reduced Pd surface as the necessary active site for catalysis, arising from the in situ reduction of the PdO_x surface sites of the air-stable hierarchical material system.