Gas Phase Hydrotreatment of Chlorophenols over Pd Catalysts as an Alternative Route to Cyclohexanone

We have established viability of cyclohexanone (C6ONE) production via coupled gas phase (1 atm, 423 K) continuous hydrodechlorination/hydrogenation of mono- and di-chlorophenols over bulk Pd and Pd/Al2O3. The catalysts have been characterised by temperature programmed reduction, H2 chemisorption, powder XRD and TEM analyses. Hydrodechlorination is not a thermodynamically limiting step where under catalytic control we achieve significantly greater C6ONE yields relative to those from standard phenol hydrogenation. We account for this response in terms of a direct chlorophenol  C6ONE conversion facilitated by electron delocalisation in the intermediate generated via electrophilic hydrogen cleavage of C–Cl bond(s). The C6ONE selectivity/conversion profiles coincided for bulk and supported Pd and we demonstrate structure sensitivity for the production of C6ONE from 2,4-dichlorophenol with higher specific rates over larger Pd particles (2→250 nm).