Unique selectivity in the hydrodechlorination of 2,4-dichlorophenol over hematite-supported Au

The gas-phase hydrodechlorination of 2,4-dichlorophenol (at 423 K) has been studied over Au/Fe2O3 prepared by deposition–precipitation. Support and catalyst were characterised by TPR, XRD, H2 chemisorption/TPD, BET area/porosity and TEM/SEM measurements. Fe2O3 was reduced to Fe3O4 and Fe following TPR to 673 K and 1273 K, respectively; inclusion of Au lowered (by 200 K) support reduction temperature. TPR of Au/Fe2O3 to 423 K generated quasi-spherical Au particles (mean size = 2.6 nm) that promoted hydrogenolysis of ortho-Cl, generating 4-chlorophenol via a stepwise mechanism. We attribute this unprecedented selectivity to reactant interaction through –OH at electron-deficient Au sites, rendering ortho-Cl susceptible to attack. Solvent effects are demonstrated for a range of carriers where conversion of aqueous 2,4-DCP delivered the highest rate (1 × 10−3 molCl h−1 image), equivalent to that achieved with Ni/SiO2 at 573 K. Selectivity in the cleavage of sterically constrained Cl in mono-, di- and tri-chlorophenols is also demonstrated.