Effect of Ag on deNO_x performance of SCR-C₃H₆ over Fe/Al-PILC catalysts

Silver has been widely used to modify the iron-based catalyst supported on alumina pillared montmorillonite to enhance its activity at lower temperature (< 300℃). Bimetallic Ag-Fe/Al-PILC (Pillared interlayer clay) was prepared by the ultrasonic impregnation method and performance was tested on a fixed bed reactor. And the experiment results showed that silver obviously improved the catalyst activity at a lower temperature. The NO conversion efficiency of Ag-Fe/Al-PILC at 250℃ was 60%, which was higher than Fe/Al-PILC (20%). The maximum 82% NO conversion and 100% N₂ selectivity were obtained by 2.1Ag-Fe/Al-PILC at 250℃. Moreover, Ag-Fe/Al-PILC revealed better anti-hydrogen peroxide and anti-sulfur dioxide ability. The catalyst characterization was conducted by several techniques with respect to the microstructure and physicochemical properties. According to the effects of N₂-adsorption and desorption tests, Ag-Fe/Al-PILC formed a stable overall structure and had a large internal specific surface area. Besides, XRD and UV-vis proved that the Ag-Fe solid solution, Ag⁺ and Ag_n^δ+ species formed on the surface of the catalyst are the key factors affecting its low-temperature activity. XPS results suggested that there was electron transfer between Ag and Fe, which formed a synergistic effect of bimetals and changed the content of Ag and Fe and their valence state on the catalyst surface. The findings of H₂-TPR indicated that the modification of Ag promoted the shift of the Fe/Al-PILC reduction peak toward low temperature, which boosted the low-temperature reduction capacity of the catalyst. The surface acidity analysis by Py-FTIR indicated that Lewis acid and Brønsted acid existed simultaneously and Ag enhanced the stability of Brønsted acid.