Catalytic Performance Of Manganese-cobalt Mixed-oxides For1,2-dichlorobenzene Catalytic Combustion At Low Temperature

A series of manganese cobalt oxides with different Co/Mn ratios were prepared by co-precipitation method and characterized by XRD, Raman, SEM, TEM, XPS and H2-TPR and so on. The catalytic combustion of1,2-dichlorobenzene (o-DCB), as a model of dioxins, was investigated in a continuous flow micro-reactor at atmospheric pressure. Effects of systematic variation of reaction conditions, including space velocity, inlet o-DCB and O2concentration, water or heptane on the catalytic combustion of o-DCB were all investigated. And the reaction mechanism was also discussed. The main results as follows:(1) Inorporation of Mn into Co3O4leads to the decrease of partical size and the increase of specific surface areas of CoxMny catalysts.(2) All Mn species substitute for Co3+ions in the octahedral sites of CoxMny catalysts with Co/Mn≥7, and one Mn4+ion will produce the additional Co2+ion.(3) Compared with pure Co3O4catalysts, manganese cobalt oxides catalysts with Co/Mn ratio above or equal to7:1were found to possess relatively higher catalytic activity, and Co9Mnl catalyst was identified as the most active catalyst and the catalytic activity of o-DCB reached90%conversion at347℃. The interface of Co3O4and MnxCo3-xO4solid solution in these catalysts provides high activity for the combustion of DCB.(4)1,2,4-trichlorobenzene (TCB) in the effluent can be detected. TCB produced on CoxMny catalysts is mainly by chlorination of o-DCB with Cl speices on the surface of catalysts. Compared with pure Co3O4, Mn-doping cobalt oxides catalysts can effectively decrease the production of the by-product TCB. Chlorination of o-DCB can also be suppressed effectively in the presence of H2O or C7H16.(5) The stability can be maintained at least35hours at370℃for the combustion of3,000ppm o-DCB concentration on Co9Mnl and Co3O4catalysts.(6) The hypothesized mechanism:Dissociative adsorption of one or two C-Cl bond of the1,2-TCB on Co-O-Co. Then, the nucleophilic lattice oxygen ions (O2-) reacts with the carbon associated with the C-Cl bond. The C-Cl bond is cleaved, and resulting in the formation of partial oxidation products. Most of which can be deep oxidated into CO2, H2O, HC1and Cl2. A little amount of them can be converted into benzene or chlorobenze through the hydrogenation dechlorination reaction.