Application of low-cost MFe2O4 (M = Cu, Mn, and Zn) spinels in low-temperature selective catalytic reduction of nitrogen oxide

One of the hottest topics in the field of selective catalytic reduction (SCR) of nitrogen oxide is to develop a catalyst with low cost, low toxicity, high activity, and good selectivity for N2 to replace high-cost and high-toxic vanadium catalyst. In this work, low-cost spinel MFe2O4 (M = Cu, Mn, and Zn) were synthesized, and applied in SCR. MnFe2O4 exhibited the best activity (99.9%) and selectivity (95.7%) at 100 °C. In comparison, CuFe2O4 was more suitable for SCR above 150 °C, and removed 94.3% of NO (950 ppm) together with a selectivity of 97.5% at the same time (150 °C). Detailed characterizations showed that the spinels were similar to each other in crystal structure, textural property, and micro-topography. Diffuse Reflection Fourier Transform Infrared spectrum indicated that the spinels all reduced nitric oxide by an Eley-Rideal mechanism. Mass spectrometry and density-functional-theory calculations revealed that different cation substitutions resulted in different abilities of NH3 dehydrogenation and over oxidization. MnFe2O4 had the lowest energy barrier (1.21 eV) for NH3 dehydrogenation, resulting in the best activity. ZnFe2O4 had a highest energy barrier (0.22 eV) for over oxidization of NH3, resulting in the best selectivity. After all, main result of this work is in favor of developing cleaner catalyst, and further works should be focused on coating the catalysts on monolithic support.