Study Of The NO Reduction By CO Over LaMn_1-xI_xO₃ Perovskites Catalysts

The noxious gases including NO_x, CO, hydrocarbons and other compounds from diesel-powered vehicles cause a series of serious environmental problems such as photochemical smog, acid rain and respiratory diseases and abatement the pollution of these exhausts have attracted much attention all over the word. Catalytic reduction of NO by CO is considered to be one of the most important approach for the control of this exhaust gas. Because most of employed noble catalysts （TWC） are facing some disadvantages such as high cost and low anti-oxidation capability. Perovskites-type catalyst has been investigated intensively because of its economic, high catalytic activity and high thermal stability.The LaMn_1-xI_xO₃ （x=0, 0.1, 0.2） perovskites with BET surface area of about 5-24 m².g^-1 were synthesized by Pechini method under various calcinations temperature and characterized by X-ray diffraction （XRD）, scanning electron microscopy （SEM）, X-ray photoelectron spectroscopy （XPS）, H₂-temperature programmed reduction （TPR） and temperature programmed desorption （TPD） of O₂, NO. The catalytic performance have been studied for the NO + CO reaction with a reaction atmosphere of 1000 ppm NO and 1000 ppm CO balanced by N₂ at a total flow rate of 400 mL/min in the 200-600℃temperature range. XRD analysis proved that all the samples were single phase crystal structure and a well-crystallised perovskite formed at 800℃, which also had the uniform morphology with a porous structure （as could be clearly observed in the SEM images）. The XPS results revealed that Mn ions were a mixed state of Mn²⁺, Mn³⁺ and Mn⁴⁺ and the valence state of substituted I ions were I⁵⁺, I substitution induced the rate of Mn⁴⁺/ Mn³⁺. H₂-TPR experiments showed that two reduction steps over the two samples, the first attributed to the reduction of Mn⁴⁺â†'Mn³⁺ and the second due to the reduction of Mn³⁺â†'Mn²⁺. The O₂-TPD profiles indicated that I doping increased the surface anion vacancy and lattice oxygen mobility.There are a lot of factors influencing catalyst catalysis performance, thesis for four of catalysis promoters for pieces of factor not main （I additive, calcination temperature, empty speed, the carbon nitrogen not empty of than） last research. The NO-TPD experiments showed that with the substitution of Mn by I, the N-containing species formed on the surface of perovskites enhanced, which provided another clue for oxygen vacancy improvement. Among the activity tests investigated, the incorporation of I into LaMnO₃ enhanced the catalytic activity of the catalyst in NO reduction by CO, and the sample LaMn_1-xI_xO₃ （x=0.1） calcined at 800°C have the best intrinsic activity on NO reduction, but decreased clearly when x was 0.2, Meanwhile, the increase of the empty speed will make NO conversion ratio reduce and CO/NO ratio have the more obviously influence at low temperature.