Sythesis Of Low Temperature And High Active α-MnO₂and The Study Of Catalytic Combustion Performance

Urban air pollutants are emerging environmental health problems in many cities of theworld. Benzene, toluene and xylene （referred to as BTXs） are pollutants, existing in indoorand air of city environments. According to the reports, BTXs can cause various diseases, suchas central nervous system leukema, respiratory system disease, cardiovascular disease andnephropathy. BTXs are constantly despoiling the human life.Catalytic combustion technology has been more and more widely used, because of itshigh efficiency and environmental protection in so much BTXs treatment method. The mostimportant part of catalytic combustion is catalyst. In this dissertation, a series of catalystswith excellent performance at lower temperature have been prepared for o-xylene catalyticcombusion. The main results are as follows:（1） A series of mesoporous α-MnO₂were successfully synthesized by KMnO₄as oxidant,Mn（Ac）₂, Mn（CH₃CH₂COO）₂, Mn（NO₃）₂, and Mn（SO₄）₂as reducing agent （the prouductsdonated as Mn-A, Mn-B, Mn-C and Mn-D, respectivily）. The effects such as bivalentmanganese salt type, pH value, instillment reagent order on the structure and activity of thecatalysts were investigated. The results showed that Mn-A, Mn-B and Mn-C can makeo-xylene completely transformed to CO₂and H₂O at210℃. However, Mn-D is higheramost30℃than those of the other three. X-ray diffraction （XRD）, Infrared radiation （IR）,Thermogravimetry （TG）, Brunauer-Emmett-Teller （BET）, Scanning electron microscopy（SEM）, Energy dispersive X-ray detector （EDX）, X-ray photoelectron spectroscopy （XPS）and chemical analysis were used to characterize the catalysts. The results showed that Mn-A,Mn-B, Mn-C and Mn-D were all mesoporous octahedral molecular sieve type α-MnO₂.Nevertheless, Mn-A and Mn-B contained almost100%Mn⁴⁺ion on their surface andpresented good mobility of lattice oxygen. Moreover, they almost had no hydroxide groupor H₂O. So, Mn-A and Mn-B have good catalyst acitivity. Mn-C contained both Mn⁴⁺ionand Mn³⁺ion, with rich hydroxy and large specific surface area, which resulted in it highactivity at low temperature. Comparing with the other catalysts, Mn-D is similar to Mn-C,but it had poor mobility of lattice oxygen and low surface oxgen content, leading to its verylow catalytic activity. （2） Three dimensional mesh structure of mesoporous α-MnO2were successfullysyMnO₂hesized by hydrothermal heterogeneous reaction method using KMnO₄and MnPO₄.Effects of mole ratio of reactaMnO₂s, reaction temperature, reaction time, calcination temperatureon the structure and activity of the catalysts were investigated. ExperimeMnO₂al results showedthat the special structure mesoporous octahedral molecular sieve type α-MnO2could beprepared as follows:10mmol KMnO₄, and10mmol MnPO₄with molar ratio ofKMnO₄/MnPO₄=1:1, at180℃for48hours. XRD, IR, BET, SEM, EDX and chemicalvalence states of manganese with chemical analysis were used to characterize the materials.The results showed that the specific area and average diameter of the material were153.12m2/g and18nm, coMnO₂aining almost100%Mn4+ion. At the same time, the morphlogyformation mechanism showed that PO₄^3-plays an importaMnO₂role on three-dimensionalstructure.（2） On the basis of mesoporous α-MnO2with three dimensional mesh structure, theproperty of catalyst was doped with K by refluxing KOH method. Moreover, Ce-Mn-Ocomposite materials were also prepared using hydrothermal syMnO₂hesis method. The resultsshowed that the catalyst were prepared with molar ratio of K/Mn=0.5:1and Ce/Mn=0.1:1,could make o-xylene completely transformed iMnO₂o CO₂and H₂O, respectively, at240℃and270℃.This dissertation was supported by the National Natural Science Founadation of China（No.21147004）, the National Natural Science Founadation of Hebei （No. B2013205100） andthe Science Foundation of Hebei Normal University （No. L2010Z06）.