Cu-zeolite catalysts for NOx removal by selective catalytic reduction with NH3 and coupled to NO storage/reduction monolith in diesel engine exhaust aftertreatment systems

•DeNOx performance of coupled NSR-SCR systems based on Cu/zeolites are compared.•NSR-SCR tests are performed with Cu-SCR granulated and monolith catalysts.•NSR-Cu/CHA achieved higher DeNOx efficiency and much higher hydrothermal resistance.•NSR-Cu/CHA achieves total NOx-to-N2 conversion with no NH3 slip, from 220 to 380 °C.

Coupled NSR-SCR systems comprising a Pt-BaO/Al2O3 NSR monolith and Cu/CHA, Cu/ZSM-5 or Cu/BETA SCR catalysts are prepared and tested for NOx removal from diesel and lean burn engines exhaust gases. The Cu/zeolite catalysts are characterized by ICP-AES, XRD, N2 adsorption-desorption, NH3-TPD and H2-TPR. The physico-chemical characteristics of fresh catalysts and aged under 5% steam/Ar at 750 °C for 16 h and are compared, resulting in the Cu/CHA with much higher hydrothermal resistance to the loss of textural and structural properties. The single-SCR, single-NSR and coupled NSR-SCR catalytic performance is studied including the conversion of NO and NH3, slip of NH3, and N2O and NO2 yields. Cu/CHA presents the SCR wider temperature window, eventually 100% NO conversion from 220 to 380 °C, even maintained after severe aging. For application in the NSR-SCR technology, the NH3 generated in the NSR catalyst during the rich period is able to achieve higher NO conversion reducing significantly the slip of NH3 (negligible at 200 °C and above), very few amount of N2O at any temperature, and small production of NO2 only at higher temperatures. This improvement of activity and selectivity is particularly enhanced with the coupled NSR-Cu/CHA system, which is also maintained when the catalyst is deposited on the cordierite monolith substrate, as in the case of real application.

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