Study On Simultaneous Catalytic Removal Of Pm-NO_x From Diesel Engine Exhaust Over A₂ BO₄-type Complex Oxides

Diesel engine as one of car power have been widely used, and the exhaust emissions problem become more and more serious situation. In lean burn condition, the main exhaust pollutions are carbon particles and NOx. Since the two things have different formation conditions, single Purification machine can not reach the demand of increasingly severe emission regulations. And the traditional method of post-processing needs the combined use several methods, cumbersome and complex. Thus simultaneous catalytic removal of PM-NOx from diesel engine exhaust becomes a hot topic in the field. The research works in this paper are summarized as follows:A series of A₂BO₄-type complex oxides L(aSr)BO₄(B=Mn,Fe,Co,Ni,Cu),La_2-xSr_xCuO₄(x=0.1,0.2,0.3,0.4,0.5,),La₂Cu_1-xFe_xO₄(x=0.1,0.2,0.3,0.4,0.5)以及La₂Cu_0.8B_0.2O₄(B=Mn,Fe,Ni) were prepared by the citric acid-liquated combustion method. These samples were characterized by means of XRD, TG-DTA, XPS, H2-TPR, NO-TPD and the catalytic activity of the catalysts for simultaneous removal of soot particulate and NOx were evaluated by a technique of the temperature-programmed reaction. The results showed that:A₂BO₄-type complex oxides have high activity in simultaneous catalytic removal of PM-NOx. For La₂CuO₄ partly substitute of La or Cu has regulation effect on catalytic activity. Sr partly replaced A-bit is negative to the active of PM-NOx catalyst reaction while Fe partly replace B-bit is on the opposite. Through compare H2-TPR data with activity evaluation data we found, theoxygen activity ability of A₂BO₄ complex oxides affected the activity of simultaneous removal of PM-NOx. To La₂CuO₄ samples, for example, Fe partly substituted B-bit of La₂CuO₄ found: in activity evaluation, strong oxygen activity ability corresponded with the relatively badly NO conversion rate. But the result of A-bit partly substituted was on the opposite. The combustion temperature of carbon particle generated CO only more close to ignition temperature of CO and NO reduction reaction can the higher activity of simultaneous catalyst removal PM-NOx occurred; otherwise, we could not achieve the purpose of simultaneous removal of both of them.In the reaction of simultaneous removal PM-NOx, from the XPS data showed: For La₂Cu_1-xFexO₄ catalyst, the stronger of lattice oxygen mobility, the higher NO conversion rate. From the NO-TPD data we also found that NO adsorption capacity increase with the lattice oxygen (Ol) volume increases. The greater amount of NO adsorption, lower temperature of the second NO-TPD desorption peak as well as increasing NO conversion rate. Showed that the stronger the lattice oxygen mobility, the higher activity of catalyst for simultaneous removal of PM-NOx.