Selective catalytic reduction of NOx over Cu- and Fe-exchanged zeolites and their mechanical mixture

SCR-NH3 activities of Cu-SAPO-34 (Cu-CZC) and Fe-Mordenite (Fe-MOR) and their mechanical mixture (50:50) were investigated in the temperature range 150-450 degrees C using operando FTIR spectroscopy. Structural and textural studies assessed the quality of the material synthesis, while in situ IR characterisation allowed the quantification of the acidic sites at the surface of the zeolites, as well as the cationic distribution inside the pores. As expected, Cu-CZC showed high NO activity at lower temperatures (75% of NO,, conversion at T < 300 C), while Fe-MOR was more active ( > 85%) at higher temperatures (300-450 degrees C). The co-presence of Cu and Fe in the mechanical mixture catalyzes the undesirable oxidation of ammonia and leads to the formation of NO, especially at high temperatures. However, the mechanical mixture of Cu-CZC and Fe-MOR has been found to efficiently operate in the presence of excess ammonia (NH3/NO = 1.3) in a much broader temperature range comparing to the catalysts modified with only one transition metal (Fe or Cu) and also respect to a sample containing both cations in a single zeolitic framework, thus opening new opportunities in the catalytic reduction of NOx,.