Experimental Study on SCR‑C3H6 Over Cu–Fe/Al-PILC Catalysts: Catalytic Performance, Characterization, and Mechanism

The selective catalytic reduction of NO with hydrocarbons (SCR-HC) is currently one of the promising technologies for the control of nitrogen oxides (NO x ). Iron-based catalysts are very promising for the SCR-HC reaction considering both the NO conversion efficiency and low cost as an environmentally friendly metal. However, these Fe-based catalysts showed poor SCR activity below 300 °C. To improve the reactivity of the iron-based catalysts supported on Alumina-pillared clays at lower temperatures, Cu was used to modify the Fe/Al-pillared interlayered clay (PILC) catalysts and the selective catalytic reduction of NO with C3H6 (SCR-C3H6) was investigated at 150–550 °C over xCu–Fe/Al-PILC catalysts (x = 0.11–0.38, x means the molar ratio of Cu/Fe) prepared by the impregnation method. The catalysts were characterized by means of X-ray diffraction (XRD), N2 adsorption–desorption, H2-temperature-programmed reduction (TPR), ultraviolet–visible spectroscopy (UV–vis), X-ray photoelectron spectroscopy (XPS), pyridine-adsorption infrared spectroscopy (Py-FTIR), etc. The results showed that Cu improved the SCR of NO obviously at lower temperatures, e.g., the NO conversion increased from 5 to 44% at 150 °C and from 15 to 93% at 250 °C, respectively, for the original Fe/Al-PILC catalysts and the 0.13Cu–Fe/Al-PILC catalyst. The interaction of copper and iron promoted the dispersion of iron species on the catalyst surface and improved the reduction ability of the iron species at lower temperatures. An appropriate copper–iron molar ratio can promote the dispersion of iron species to obtain a larger specific surface area and pore volume. Cu improved the formation of isolated Fe3+ and Fe2O3 particles, and the former together with the isolated Cu2+ contributed to the reduction performance at low temperatures, while the latter allowed the catalyst to maintain a high NO conversion at high temperatures. Moreover, Cu increased the surface acidity of the catalysts. A possible reaction pathway was proposed based on an in situ diffuse reflectance Fourier transform infrared spectroscopy (in situ DRIFTS) study, where the active species were mainly monodentate nitrates, acetates, and NCO species. Importantly, the introduction of Cu promoted the formation of more of these active species, which were contributed to the activity of C3H6-SCR.