Manganese-based Composite Oxides For Catalytic Oxidation Of VOCs

In recent years,haze has become a serious air pollution problem.Volatile Organic Compounds(VOCs)emitted by many industrial processes are a major factor of ozone pollution and.Meanwhile,VOCs can cause a range of adverse effects on human body,such as headaches,respiratory and skin irritation,even causing cancer.Catalytic oxidation technology is one of the most effective methods of VOCs treatment Manganese oxides have unique redox properties due to its various crystal structures and abundant oxidation states,which is beneficial to the utilization of surface oxygen and activation of gaseous oxygen during the process of catalytic oxidation,so it is widely applied in the field of catalysis.In this thesis,manganese-based composite oxides with different structures and components are prepared by different methods,and further investigate their performance on catalytic oxidation of typical VOCs(such as benzene and formaldehyde).By means of composition and structure regulation,the relationship between structure and performance is explored.The main research results are as follows(1)Preparation of perovskite LaMnO3 catalyst and its catalytic performance for benzeneLaMnO3 with different morphologies and good crystallinity was prepared by sol-gel method,hard template method,microemulsion method and precipitation method respectively.LaMnO3 prepared with silicon dioxide KIT-6 as template had the maximum specific surface area(108.8 m2 g-1).The multichannel structure of template was well preserved and its performance of catalytic oxidation for benzene was the best(T90%=237?)WHSV=60000 mL g1-h-1).The catalytic performance of LaMnO3 prepared by different methods were ranked as follows:hard template method>sol-gel method>precipitation method>microemulsion method,and the results of analysis indicate that specific surface area and pore structure were the key factors affecting the catalytic activity of LaMnO3(2)Preparation of Cu-Mn composite oxides containing spinel phase and its catalytic performance for benzeneA series of Cua3-xMnx(x=0,1,1.5,2,2.5,3)copper manganese oxides containing spinel phase were prepared by sol-gel method.The effect of spinel phase formation on the catalytic activity of benzene was investigated.CuMn2 was mainly composed of spinel phase CuMn2O4 and Mn2O3.The formation of spinel phase brought with larger specific surface area,smaller pore size and more lattice oxygen,which significantly improved the activity and stability of benzene catalytic oxidation.CuMn2 exhibited the best catalytic performance at low temperature(T90%=186?).The results showed that CuMn2O4 played an important role in promoting electron transport and lattice oxygen migration.(3)Preparation of CeO2@MnOx core-shell structure catalyst and its catalytic performance for benzeneCeO2 nanotubes were obtained by partial pyrolysis of Ce-MOF(Metal Organic Framework,MOF),and then coated with manganese oxide by self-deposition through redox.CeO2@MnOx catalysts with different Mn/Ce ratios were successfully prepared to further explore their catalytic performance for benzene oxidation.Among these,when the mole ratio of Mn/Ce was 2.03,manganese oxide coating in the CeO2@MnOx was uniform,forming a hollow core-shell structure with high specific surface area(203.8 m2 g-1)and uniform mesoporous distribution.In addition,it had good low temperature reducibility,abundant oxygen vacancy and acid sites,high content of Ce3+,Mn4+ and adsorbed oxygen species,which contributed to the enhancement of catalytic activity.The catalyst showed the best catalytic performance for 100 ppm benzene at the mass airspeed of 60000 mL g-1 h-1(T90%=148?),the low-temperature catalytic performance preceded latest reported precious metal catalysts(4)Preparation of monolithic catalyst and its catalytic performance for formaldehyde under microwaveA series of cordierite supported(LaMnO3,LaMnO3/CeOx,LaMnO3/ZrCeOx,CuOx/MnOx)catalysts(size 10 × 10 × 5 cm)were prepared by a simple impregnation method.The results showed that all monolithic catalysts had good microwave absorption ability,among which cordierite supported LaMnOx catalyst had the best overall microwave absorption effect and can heat up to 200? in about 7 minutes under the microwave power of 300 W.Cordierite supported CuOx/MnOx catalyst had the highest catalytic rate under the microwave power of 300 W.Cordierite supported LaMnO/ZrCeOx catalyst had the best catalytic effect on formaldehyde at low temperature,it was expected to completely degrade lppm formaldehyde at 100?(volume space velocity,20000 h-1).