On the Cu species in Cu/beta catalysts related to DeNOx performance of coupled NSR-SCR technology using sequential monoliths and dual-layer monolithic catalysts

• NH3-SCR activity is related to Cu species and oxidation state.
• Washcoat loading is optimized for NSR and SCR monoliths.
• Top layer SCR loading can be tuned to enhance DeNOx performance of dual-layer devices.
• DeNOx performance of sequential NSR-SCR monoliths and dual-layer monolith is compared.

Cu/beta catalysts are prepared starting from protonic or ammonic BEA zeolite following liquid ion exchange with copper. Alternatively, an intermediate ion exchange with Na ions is performed before copper ion exchange. Cu/beta catalysts are extensively characterized by XRF, N2 adsorption–desorption, FT-IR of NO and CO adsorption, EPR, H2-TPR, TEM and SEM in order to identify copper oxidation state (Cu+ or Cu2+) and copper species (agglomerated or Cu ions with different interaction with the support). Cu/beta catalyst prepared from ammonic BEA zeolite with intermediate Na ion exchange followed by copper ion exchange results in the most active catalyst in the NH3-SCR reaction, which is related to the coexistence of Cu+ and Cu2+ ions and to a more accessible location of such ions in the zeolite matrix. This catalyst is washcoated onto a monolithic substrate with an optimum loading of 0.32 g cm−3, in order to be placed downstream a NOx storage and reduction (NSR) monolithic catalyst, prepared by washcoating Pt-Ba/Al2O3 powder with an optimum loading of 0.25 g cm−3. NSR-SCR catalyst in sequential beds results in a very active system with a NOx removal of 97% and a N2 selectivity of 96% at 275 °C. NSR/SCR catalyst prepared in a unique dual layer device shows that top SCR layer loading can be tuned in order to improve DeNOx performance. Optimum SCR layer loading is observed for 0.02 g cm−3, enhancing the NOx to N2 efficiency of single NSR catalyst but far away from the catalytic performance observed for the sequential NSR-SCR configuration.

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