Study On The Perovskite-type Catalyst For Catalytic Oxidation Of CO

As people are paying more and more attention to environmental pollution,the treatment of air pollution has become particularly important.CO is one of the main components in the exhaust gas of motor vehicles or flue gas from industrial process like iron ore sintering.The removal of CO from flue gas has always been a research hotspot.As a kind of ceramic oxide with ABO₃ structure,perovskite has broad element accommodation,high thermal and chemical stability.It has high catalytic activity for the complete oxidation of inorganic molecule like CO.Therefore,perovskite-type materials have received more and more attention in the researches of catalysts in recent years.In this work,the performances of different types of perovskite catalysts in the catalytic oxidation of CO are mainly studied.The main goal of this work is to reduce the temperature value of CO complete oxidation through the improvement of the preparation method and the design of the catalyst composition.Firstly,La_1-xSr_xCo O₃（x=0,0.2,0.4,0.6,0.8）perovskite catalyst was prepared by flame spray synthesis（FSS）method.The activity of doped catalyst is studied by kinds of characterization methods and catalytic oxidation experiments.The results show that the activity of La_1-xSr_xCo O₃ catalyst prepared by FSS method is higher than the same kind of catalyst prepared by other conventional methods.La_0.4Sr_0.6Co O₃ shows the highest activity in CO catalytic oxidation,in which the temperature values of 50%and90%CO conversion are T_50%=148.6°C and T_90%=165.9°C,respectively.Due to the limit of the solubility of perovskite structure,the activity of catalyst can not be further improved when the doping amount of Sr²⁺is 0.8.The results of CO consecutive catalytic oxidation reactions show that La_1-xSr_xCo O₃ prepared by FSS method has good catalytic stability.Secondly,La Mn_1-xCu_xO₃（x=0,0.2,0.4,0.6,0.8）perovskite catalyst was also prepared by FSS method.The doping of Cu²⁺in B site improves the mean particle diameter and the specific surface area（SSA）of catalyst and makes the reduction of Mn³⁺easier.The catalyst has the highest activity when x=0.6 and T_50%=157.4°C,T_90%=178.6°C in the reaction.The perovskite phase of the catalyst phase composition is no longer the main component and the SSA decreases when x=0.8.Therefore,the activity of La Mn_0.2Cu_0.8O₃ is lower than that of La Mn_0.4Cu_0.6O₃.After eight consecutive CO catalytic oxidation cycles,La Mn_1-xCu_xO₃ catalyst can still maintain good catalytic activity.Finally,the supported catalysts of La Mn O₃ perovskite with HZSM-5 zeolite as support were prepared by sol-gel method.The effects of 20%,40%,60%,80%and 100%of different perovskite loading amounts on the activity of supported catalysts were studied.The results show that the HZSM-5 zeolite support can greatly increase the SSA of the perovskite catalyst and improve the catalytic activity.When the loading amount of perovskite is 60%,60LM/HZSM-5 catalyst has the best catalytic activity in CO oxidation reaction,in which T_50%=172.7°C and T_90%=201.5°C.When the loading amount increases to 80%or 100%,the activity of catalyst decreases due to the decrease of SSA caused by the accumulated pores of loaded perovskite.In the CO consecutive catalytic oxidation cycles,the increase of T_{50%or 90%}of the catalyst in the 8th cycle reaction is lower than 20°C compared with the first time.The results indicate that the LM/HZSM-5 supported catalysts also have good catalytic stability.