Selective Hydrogenation of Phenol to Cyclohexanone over Pd-HAP Catalyst in Aqueous Media

The production of pure cyclohexanone under mild conditions over catalysts with high reactivity, selectivity, compatibility, stability, and low cost is still a great challenge. Here we report a hydroxyapatite-bound palladium catalyst (Pd-HAP) to demonstrate its excellent performance on phenol hydrogenation to cyclohexanone. Based on catalyst characterization, the Pd nanoclusters (approximate to 0.9nm) are highly dispersed and bound to phosphate in HAP. Only basic active sites on HAP surface are detected. At 25 degrees C and ambient H-2 pressure in water, phenol can be 100% converted into cyclohexanone with 100% selectivity. This system shows a universal applicability to temperature, pH, solvent, low H-2 purity, and pressure. The catalyst reveals high stability to be recycled without deactivation or morphology change; and Pd nano-clusters barely aggregate even at 400 degrees C. During the reaction, HAP adsorbs phenol, and Pd nanoclusters activate and spillover H-2. The mechanism is also investigated, proposed, and verified.