Sythesis Of α-MnO₂Nanophase And Their Application In Catalytic Oxidation Of O-xylene

Benzene hydrocarbons （such as benzene, toluene and xylene） are the major organicvolatile compounds （VOCs） in the air. They were mainly vented form a variety of industrial,such as chemical production, mobile emission and family decorate, which cause serious harmto human health. Therefore, the removal of benzene pollutants has become an importantresearch in topic recent environmental treatments. Deep catalytic oxidation that can directlyoxidize benzene pollution into CO₂and H2O is one of the most effective and promisingresearch methods. The manganese oxides are regarded as important catalysts due to theirlow-priced. Therefore preparation of the catalysts with high activity used in the completecatalytic oxidation of benzene pollutants is a very significant subject.In this paper, α-MnO₂nanowires were prepared using hydrothermal method. Theα-MnO₂nanowires were used for o-xylene deep catalytic oxidation. The catalytic activitieswere evaluated in term of o-xylene conversion and the yield of CO₂. X-ray diffraction （XRD）,Scanning electron microscopy （SEM）, Brunauer-Emmett-Teller （BET）, Transmission electronmicroscopy （TEM） and Energy dispersive spectrometer （EDS） were used to characterize thecatalysts. The main results are as follows:1Mesoporous α-MnO₂nanowires were successfully synthesized by hydrothermalmethod based on the redox reactions of KMnO₄and MnCO₃. The influence of the reactiontemperature, reaction time and concentration on the product phase and morphology of theobtained α-MnO₂nanowires were discussed. Experimental results showed that α-MnO₂nanowires could be prepared under the conditions:10mmol KMnO₄,-and10mmol MnCO₃with molar ratio of n（KMnO₄）:n（MnCO₃）=1:1, at180oC for12h. The BET results showedthat the specific area and average diameter were140.012m²Â·g^-1and20nm, respectively,which belong to mesoporous structure. The catalyst calcined at500oC could converseo-xylene into carbon dioxide and water at200oC.2One dimensional structure of α-MnO₂nanowires were successfully synthesized byhydrothermal method using potassium permanganate KMnO₄and MnCO₃as raw materials.The reactants conditions were as follows: n（KMnO₄）:n（（NH₄）₂CO₃）=1:3,120°C,12h. The influence of the reactant molar ratio, reaction temperature, reaction time and concentration onthe product phase and morphology of obtained α-MnO₂nanowires with one dimensionalstructure were discussed. The CO₂gas which produced by heating （NH₄）₂CO₃play animportant role in the formation of catalyst.3On the basis of α-MnO₂nanowires with one dimensional structure, the property ofcatalytic were changed by the impregnation method, such as KNO₃, Ce（NO₃）₃·6H₂O,Cu（NO₃）₂·3H₂O, Fe（NO₃）₃·9H₂O, Al（NO₃）₃·9H₂O and Ni（NO₃）₂·6H₂O solution. The resultshowed that catalysts could converse o-xylene into carbon dioxide and water at220°C、240°C、240°C、320°C、320°C and310°C.This paper was funded by the funds of national natural science （NO.21147004）.