DRIFTS study of γFe 2 O 3 nano‐catalyst for low‐temperature selective catalytic reduction of NO x with NH 3

The catalysts used in the selective catalytic reduction (SCR) of NO x with NH 3 were prepared from γFe 2 O 3 nanoparticles. The NH 3 ‐SCR activity measurement was carried out in a fixed bed reactor. The adsorption characteristics of γFe 2 O 3 nano‐catalysts to NH 3 and NO were studied with in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) measurements. Experimental activity measurement indicated that γFe 2 O 3 used as a SCR de‐NO x catalyst exhibited excellent low‐temperature SCR de‐NO x performance. The DRIFTS measurements showed that there existed both NH 4 + bonded to Brønsted acid sites and coordinated NH 3 bonded to Lewis acid sites on the catalyst surface. Coordinated NH 3 was the main adsorption product. O 2 promoted H‐abstraction from coordinated NH 3 to form NH 2 species, as well as O 2 greatly enhancing the adsorption of NO on the catalyst surface to form nitrate species and absorbed NO 2 . Possible reaction paths with the γFe 2 O 3 catalyst were proposed as follows: the SCR process mainly formed NH 2 from H‐abstraction of coordinated NH 3 which reacted with NO to form N 2 and H 2 O at high and medium temperatures. At low temperatures, however, the formation of adsorbed NO 2 resulted from NO oxidation by O 2 over Fe 3+ sites played an important role. NH 4 NO 3 and (NH 4 + ) 2 NO 2 as the key intermediate products reacted with NO to form N 2 and H 2 O at low temperatures.