Research On Low-temperature Selective Catalytic Reduction Of No With NH₃Over Supported Perovskite-typed Oxides

Selective catalytic reduction （SCR） with NH3as a reductant has beencommonly applied to reduce NO_xemissions from the stationary sourcessuch as power plants for several decades. In this study, in light ofperovskite oxides having many advantages such as excellent thermalstability, superior redox properties, great versatility and low cost, a seriesof perovskite oxides catalysts would be subjected to the SCR activity test,The optimal perovskite would be selected and loaded on differentsupports to determine the novel catalyst candidates for the SCR of NOwith NH3at low temperature.A series of ABO₃or A₂BO₄perovskite-type catalysts with differentB-site ions （B=Mn, Cu, Fe, and Co） was prepared and characterized byXRD, BET, H₂-TPR, NH3-and NO+O₂-TPD, and in-situ DRIFTs. It wasfound the capacity of absorbing NH3and the stability of NO_xad-speciesupon perovskites were decisive factors for the SCR activity of theperovskite catalysts, and Mn-based perovskite had the best catalyticperformance, yielding78%NO conversion at250oC and30700h^-1. According to the activity comparison between LaMnO₃and Mn-basedsimple oxides，it could be concluded that the crystal structure of ABO₃perovskite had a remarkable promotion effect on the SCR process.TheSCR reaction occurring on the surface of LaMnO₃involvedLangmuir-Hinshelwood mechanism.Furthermore, the SCR activities of La0.9A′0.1Mn1-xB′xO3（A′-Sr, Ce, K;B′-Cu, Fe, V; x=0,0.05,0.1,0.5） was also investigated, it was obtainedthat the substitution of Ce for A-site element （La） and the substitution ofCu or Fe for B-site element （Mn） in LaMnO₃would improve significantlythe activity in low-temperature range （<200oC） and high-temperaturerange （>200oC）, respectively. Mn-based perovskites supported ondifferent supports MOx（M-Al, Zr, Ti, Ce） were subjected to activity testto select the optimum support. The interaction between CeO₂andLaMnO₃enhanced the SCR activity particularly in the low-temperaturerange, and the ratio of Ce to Mn was a key factor to influence the SCRperformance. TiO₂supported perovskites were benifical for improving N2selectivity, but were poor at increasing the NO conversion. In this study,the best catalyst for the SCR reaction was LaMnO3supported on CeO₂with the loading of40%, which achieved100%NO conversion at200oC.