NiMn2O4 sphere catalyst for the selective catalytic reduction of NO by NH3: Insight into the enhanced activity via solvothermal method

Abstract

Herein, NiMn2O4 sphere (NiMn2O4-S) and NiMn2O4 particle (NiMn2O4-P) were fabricated via solvothermal method and ammonia precipitation method followed by calcination, then the two samples were evaluated as potential candidate catalysts for low temperature NH3-SCR. Meanwhile, systematical characterizations were employed to establish the relationship between denitrification performance and physiochemical properties. Besides, in-situ DRIFTs and kinetics calculation were performed to reveal the reaction mechanism and the intrinsic catalytic activity. The results verified the preferable catalytic performance of NiMn2O4-S with higher than 90% NO conversion at the range of 85–285 °C, and nearly 100% N2 selectivity at 120 °C. The fine catalytic activity might be related to the larger specific surface area, which could contribute to higher Mn4+/Mnn+ ratio, ampler Oα, more suitable acid amounts and redox capacity. In-situ DRIFTs revealed that the NH3-SCR over NiMn2O4-S and NiMn2O4-P catalysts mainly preceded via Eley–Rideal (E–R) mechanism at 90 °C. The higher TOF values and lower Ea value for NiMn2O4-S catalyst further confirmed its excellent de-NOx performance. As compared to NiMn2O4-P catalysts, the hierarchical spherical morphology of NiMn2O4-S catalyst could generate even more abundant NH3/NOx adsorption sites, higher reactivity of NH4+ bounded to Brønsted acid sites (NH4+-BASs) and NH2 species which were conducive to the enhancement of low temperature activity.