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

• Published in: Journal of catalysis 2013-07, Vol.303, p.41-49
• Main Authors: Gómez-Quero, Santiago, Cárdenas-Lizana, Fernando, Keane, Mark A.
• Format: Article
• Language: English
• Subjects: 2,4-Dichlorophenol; Au/Fe2O3; Catalysis; catalysts; Chemistry; Chlorophenol(s); Exact sciences and technology; ferric oxide; Gases; General and physical chemistry; gold; hydrogen; Inductive effects; iron; Nanoparticles; Phase transitions; porosity; scanning electron microscopy; Selective hydrodechlorination; solvents; temperature; Theory of reactions, general kinetics. Catalysis. Nomenclature, chemical documentation, computer chemistry; transmission electron microscopy; X-ray diffraction
• ISSN: 0021-9517; 1090-2694
• DOI: 10.1016/j.jcat.2013.03.011

Nano-scale Au on Fe2O3 promotes selective hydrogenolysis of sterically constrained ortho-Cl from 2,4-dichlorophenol in continuous gas-phase operation. •TPR of Au/Fe2O3 to 423K generates Au nanoparticles (mean size=2.6nm).•First reported application of Au/Fe2O3 in catalytic hydrodechlorination.•Au/Fe2O3 promotes selective hydrogenolysis of ortho-Cl in 2,4-dichlorophenol.•Water as carrier delivers highest dechlorination rates.•Selective cleavage of sterically constrained Cl in mono-, di- and tri-chlorophenols. The gas-phase hydrodechlorination of 2,4-dichlorophenol (at 423K) 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 673K and 1273K, respectively; inclusion of Au lowered (by 200K) support reduction temperature. TPR of Au/Fe2O3 to 423K generated quasi-spherical Au particles (mean size=2.6nm) 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 (1×10−3molClh−1mAu-2), equivalent to that achieved with Ni/SiO2 at 573K. Selectivity in the cleavage of sterically constrained Cl in mono-, di- and tri-chlorophenols is also demonstrated.