Study On Manganese-based Perovskite-type Complex Oxides Catalysts For The Purification Of Fcc Flue Gases

Nitrogen oxides(NOx)are discharged from the FCC flue gases in the process of FCC catalysts regeneration,accompanied with a certain amount of carbon monoxide due to the imcomplete burning of coke over FCC catalysts,which fouls the atmospheric environment.So it is of significance to develop highly efficient catalysts for NOx removal and soot combustion.In this paper,manganese-based perovskite-type oxides catalysts were prepared by a hydrothermal method,also ZSM-5 supported manganese-based perovskite catalysts by an equal volume impregnation method,and characterized with XRD,FT-IR,NO-TPD,SEM,H2-TPR,BET and XPS.And the activity of catalysts was evaluated in a fixed-bed micro-reactor.Based on in situ DRIFTS technology,the process of NOx-soot reaction was preliminarily investigated.Conclusions were as follows:1.The optimal synthesis conditions for the manganese-based perovskites type complex oxides were obtained with ethanol to water volume ratio of 12:2,crystallization temperature of 180 ?,crystallization time of 8 h and urea of 112.50 mmol.After calcining of precursor,the obtained catalyst showed the best catalytic performance for NOx-soot removal with the NO conversion of 37.8%at 450 ? as well as the soot ignition at 350 ? with the SCO2 of 99.1%.2.After alkali metal ions doping at A site of LaMnO3 perovskite,the catalytic performance of catalysts were changed for NOx-soot removal.After Na doping,no obvious improved performance was observed.The catalytic performance of catalysts was polished up after introduction of Li,K and Rb,among which Rb doping was the best.When the doping amount of Rb was 0.25,the catalytic performance of catalyst was the most optimal with NO conversion of 60.9%,soot was ignited at 314 ? with 98.9%of SCO2.3.The ZSM-5 supported perovskite catalysts were prepared by an equal volume impregnation method.The experimental results showed that the good performance of NOx-soot removal was obtained over LaMnO3(10)/ZSM-5(300)catalyst with max NO conversion of 46.0%at 480 ?,the soot combustion temperature such as Tig,Tmax and Tf was 380 ?,513 ? and 569 ?,the selectivity of carbon dioxide was 97.7%.After introduction of K at A site,the performance of catalyst for soot combustion was slightly improved,however,the catalytic performance of NOx removal was pulled down with the maximum NO conversion of only 44.0%compared with LaMnO3(5)/ZSM-5(300).4.In situ DRIFTS reaction investigation.The experimental results showed that the main NOx adsorped species over catalyst were free nirate ions,ionic nitrate and monodentate nitrate,among which ionic nitrate was the most stable.In the presence of oxygen molecules,soot began to react with ionic nitrate at 350 ? to form nitrogen and carbon dioxide,achieving the goal of NOx-soot removal at the same time.