Tailoring the Low-Temperature Denitrification Window of Mncrni Catalysts Through Ni Source Engineering: The Effect of Nickel Precursors on Activity

Abstract

Catalysts operate at various temperatures under differing operational conditions, underscoring the significance of developing catalysts that can be specifically tailored to optimize denitrification within targeted temperature ranges. In this study, the catalysts MnCr0.7Ni0.3-n and MnCr0.7Ni0.3-c demonstrated conversion rates of 96% within the temperature ranges of 150-200 °C and 200-250 °C, respectively. The catalytic activity of MnCr0.7Ni0.3-c can achieve 88% conversion in the presence of 100 ppm NO and 10 vol% H2O. Characterization results indicate valence transitions between Cr6+ and Cr3+and between Ni3+ and Ni2+in MnCr0.7Ni0.3-n. These transitions facilitate electron migration and the formation of electron vacancies or unsaturated bonds. MnCr0.7Ni0.3-n presents a greater number of acidic active sites, which enhances the reaction between adsorbed NH3 and NO on the catalyst surface. Conversely, MnCr0.7Ni0.3-c possesses a higher content of Oα, leading to stronger interactions that produce more oxygen vacancies and unsaturated bonds. Additionally, the higher density of strong acidic sites in MnCr0.7Ni0.3-c facilitates the selective catalytic reduction (SCR) reaction more effectively at elevated temperatures. Density Functional Theory (DFT) studies reveal that electron transfer occurs between the oxygen atoms in NO, NO2, and SO2 and the surrounding Mn sites, resulting in increased bond lengths among the gas molecules and promoting gas adsorption. Notably, there is no significant resonance interaction between NO, H2O, and NO2 with the MnO (110) surface, which leads to the formation of ionic bonds.

Keywords: NH3-SCR, MnCrxNi1-x-n/c, Different Ni modulations, DFT