Cu- and Fe-speciation in composite zeolite catalyst for selective catalytic reduction of NO x : insights from operando XAS

International audienceCu-SAPO-34 (Cu-CZC) and Fe-Mordenite (Fe-MOR) and their mechanical mixture (50:50) have been exhaustively investigated by means of operando X-ray absorption spectroscopy under NH3-SCR conditions. Fe K-edge XANES and EXAFS analysis revealed similar Fe-speciation in both pure Fe-MOR catalyst and the mechanical mixture after high-temperature pretreatment and under reaction conditions. In contrast, analysis of the Cu K-edge dataset unveiled essentially different trends in temperature-driven Cu-speciation in the pure Cu-CZC and mechanical mixture under standard NH3-SCR conditions. This difference is more evident in the low-temperature range. The presence of Fe-MOR counterpart in the mixed catalyst can result in the increase of NH3 an NO concentration in proximity of Cu-sites, which facilitates temperature-driven migration of NH3-solvated mobile di-amino complexes from Cu-CZC to the MOR framework. This decreases the density of mobile Cu I complexes in the entire system and results in the higher reducibility of Cu in the mixed catalyst. The obtained results help in understanding the precise speciation of the active sites in such composite catalysts and thus provides future guidance to design of such systems