Study On The NO_x Storage And Reduction Performance Of The CuO/K₂CO₃/MgAl₂O₄ Catalyst At High Temperatures

High NO_x removal efficiency has been achieved over the Pt/BaO/Al₂O₃ catalyst within a narrow temperature window of 300-400?.When the operating temperature exceeds 400?,Pt sintering and the low thermal stability of nitrates hamper the declines its application at high operating temperatures.To solve this problem,herein,we employ CuO to substitude of expensive Pt as the NO_x oxidation and reduction center,potassium as the NO_x storage element and MgAl₂O₄ as the support material,designing a new CuO/K₂CO₃/MgAl₂O₄ NSR catalyst operating at the high temperatures?350-550??.The CuO/K₂CO₃/Al₂O₃ catalyst was also prepared as a comparison.we characterized the catalysts by the X-ray diffraction?XRD?,X-ray absorption near-edge structures?XANES?,X-Ray photoelectron spectroscopy?XPS?,scanning electron microscopy?SEM?,high-resolution transmission electron microscopy?HR-TEM?,fourier-transforminginfraredspectra?FT-IR?,H₂temperature-programmed reduction?H₂-TPR?,temperature-programmed desorption of CO₂?CO₂-TPD?and temperature-programmed desorption of NO_x?NO_x-TPD?.The NO_x reduction percentage?NRP?of the CuO/K₂CO₃/MgAl₂O₄ catalyst remains above90%over a wide temperature range?400-550??,and reaches the highest NRP of99.9%at 450? with the N₂ selectivity of 99.7%.Based on our study,the CuO/K₂CO₃/MgAl₂O₄ catalyst can improve the NO_x storage capacity of K₂CO₃ and the redox ability of CuO on it.Furthermore,CuO/K₂CO₃/MgAl₂O₄ catalyst can enhance the thermal stability of nitrate formed on it in the NO_x storage stage.Therefore,the CuO/K₂CO₃/MgAl₂O₄ catalyst exhibits the high NSR performance at high operating temperatures.In this study,the effect of potassium loading on the NO_x storage and reduction performance of the catalyst was also studied.In the catalyst,the K₂CO₃ exists as highly dispersed K₂CO₃ and bulk K₂CO₃.In the lean-burn period,the nitrates formed on the bulk K₂CO₃ have high thermal stability at high operating temperature,while the thermal stability of the nitrates formed on the highly dispersed K₂CO₃ is low.When the K loading is low,the K₂CO₃ mainly exists as highly dispersed K₂CO₃,the limited NO_x storage capacity and the low thermal stability of the nitrates result in the low NSR activity at high temperature.While too much K₂CO₃ loaded on the catalyst can decrease the redox ability of CuO by covering it,which will decrease the NSR activity of the catalysts.When the K loading is 10%,the best NSR activity is obtained with the highest NO_x reduction percentage at 450?.