FeVO4-supported Mn–Ce oxides for the low-temperature selective catalytic reduction of NOx by NH3

Abstract

Iron vanadate (FeVO₄) nanorods are used as a carrier to support manganese (Mn) and cerium (Ce) oxides for the selective catalytic reduction (SCR) of nitrogen oxides (NO_x) with NH₃ for the first time. Among these developed Ce–Mn/FeVO₄ catalysts with different molar ratios of Ce/Mn, the Ce_0.2Mn_0.2/FeVO₄ catalyst exhibits the best de-NO_x performance and N₂ selectivity, which are higher than 90% in a wide temperature window of 90–420 °C. Through a series of characterization techniques, it is found that the synergistic effect between Ce and Mn enhances the reduction ability and the number of acid sites on the catalyst, which facilitates the adsorption and conversion of flue gas. The introduction of an appropriate ratio of Ce/Mn increases the concentration of Mn⁴⁺ and chemisorbed oxygen (O_S) on the catalyst, leading to a “fast SCR reaction” with oxidizing NO to NO₂, which significantly improves the low-temperature de-NO_x efficiency. In addition, the interaction between the active components (Ce/Mn) and the support (FeVO₄) increases the de-NO_x performance of Ce_0.2Mn_0.2/FeVO₄ at high temperatures. In the meantime, the Mn⁴⁺ + Ce³⁺ ↔ Mn³⁺ + Ce⁴⁺ reduction electron pair formed between Ce and Mn promotes the transport of electrons, which is also beneficial for the SCR reaction at low temperature. The in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) reveals that the SCR reaction over Ce_0.2Mn_0.2/FeVO₄ catalyst follows both Eley–Rideal (E–R) and Langmuir–Hinshelwood (L–H) reaction mechanisms.