Study On Low Temperature Denitration And Ammoxidation Of Manganese-based Composite Oxide

The emission of nitrogen oxides NO_x is one of the causes of air pollution,The selective catalytic reduction of NO with ammonia is of great significance in protecting the atmospheric environment and energy utilization.The catalyst of vanadium-titanium system has low denitration efficiency at low-temperature and contains toxic substance vanadium.Therefore,the catalysts with excellent low-temperature SCR activity become the research hightlights.In this dissertation,manganese oxide was used as the main body,and the cobalt manganese oxide catalyst was prepared by sol-gel method.The influence of different Co/Mn ratio and different calcination temperatures on the catalytic reaction was investigated.Through the study of the physicochemical properties of the catalyst,preliminary explorations have been made on the reasons for the differences in catalytic activity.In order to solve the problem of ammonia escape during the SCR reaction,Ce-MnO_x was prepared for selective catalytic oxidation（SCO）of ammonia by hydrothermal and impregnation method respectively.The effects of the two synthetic methods on the ammoxidation reaction were compared.Finally,diatomite,halloysite,and palgorskite were used to support the Mn₇Co₃ catalyst to study the effect of the support on the catalyst activity and the water and sulfur resistance.The specific results of the dissertation are as follows:（1）The Mn₇Co₃ catalyst exhibits excellent low-temperature catalytic activity.When the reaction temperature is 75 ^oC,the complete conversion of NO can be achieved and the selectivity of N₂ is above 95%,at the same time,it has good water resistance to SO₂ poisoning.The introduction of Co is beneficial to improve the redox ability of manganese oxide,and the interaction between Mn and Co promotes the progress of the SCR reaction.（2）The results demonstrated that Ce-MnO_x catalysts exhibited the best NH₃catalytic oxidation activity which composited by hydrothermal method.Ce（5）-MnO_x（HY）reached 98%NH₃ conversion and 91%N₂selectivity at 200 ^oC.The distinguished catalytic activity of Ce-MnO_x was attributed to abundant Mn⁴⁺and Ce³⁺,high surface adsorbed oxygen concentration,a large number of active sites,and strong interaction between Mn and Ce.（3）In the ammonia oxidation reaction that the-NH₂ and-NH intermediates could be generated by adsorbed NH₃ dehydrogenation.Consequently,-NH and atomic oxygen combined to form-HNO,which could be quickly oxidized by O₂ to NO.Finally,N₂ and H₂O were formed during the following reaction of NO with-NH₂.（4）Among the three carriers,the cobalt manganese oxide with diatomite carrier has relatively best SCR activity.The introduction of transition metal elements（Fe,Ni,Ce）did not failed to further improve the performance of the catalyst,but the doping of Ce inhibits the SO₂ poisoning of the catalyst to a certain extent.