Catalytic Performance and Reaction Mechanism of Chlorobenzene Oxidation over MnO_x-CeO₂ Catalyst

The influence factors (Mn/Ce molar ratio, reaction temperature, oxygen, water), physicochemical properties, interaction process and reaction mechanism are analyzed and proposed on MnOx-CeO2 catalysts for chlorobenzene oxidation performances (activity, selectivity and stability). With 5% (volume fraction) H2Ogas and 5%(volume fraction) O-2, the optimum Mn2Ce1Ox catalyst obtains the chlorobenzene conversion rate of 80.6%, 86.8% and 97.5% at 100, 200 and 300 degrees C, respectively. High reaction temperature, high oxygen content and also the presence of water are beneficial to the improvement of catalytic conversion and reaction stability. The doping procedure of MnOx and CeO2 multi-oxides increases specific surface area to 128.61 m(2)/g, decreases pore size to 6.17 nm, and strengthens surface acidity (especially at middle & strong acid sites) and also redox performance. The electron interaction (Ce4+/Ce3+<-> Mn4+/Mn3+/Mn2+) and oxygen cycle (surface adsorbed oxygen <-> lattice oxygen) are the essential driving processes to promote the catalytic oxidation. Chlorobenzene molecules are adsorbed on the surface of Mn2Ce1Ox catalyst to de-chlorinate and form phenol, in turn, the ring-opening of aromatic ring is occurred and then oxidated into the formation of most critical acetate intermediates that result in as finial as possible CO2, HCl or Cl-2, H2O. Under the activation actions of water and oxygen molecules to hydroxyl groups and active-oxygen species, the adsorption-activation of chlorobenzene and deep oxidation of intermediates are enhanced and more beneficial to reduce the generation of by-products (chloroethoxyl, phenol and aldehydes, etc.) and also Cl-containing species, thus improving the catalytic activity and reaction stability.