Effect of chelating agents on selective catalytic reduction activity and mechanism for MnCr2O4 spinel catalyst

Four different chelating agents, ethylenediamine tetraacetic acid, citric acid, glucose, and sucrose, were selected to synthesize MnCr₂O₄ catalysts (spinel structure) with sol-gel method. Among the prepared catalysts, MnCr₂O₄-S-700, which had the largest specific surface area, showed the best catalytic performance, with a T80 temperature window of 200–260 °C and a denitrification rate of up to 91.6% at 220 °C. Hydrogen temperature programmed reduction, ammonia temperature programmed desorption, and X-ray photoelectron spectroscopy results showed that MnCr₂O₄-S-700 possessed more chemisorbed oxygen O_α as well as active sites (Mn³⁺ + Mn⁴⁺) and (Cr³⁺ + Cr⁵⁺), which improved acidity and redox capacity. There was abundant electron transfer between Mn and Cr elements (Cr⁵⁺ + Mn³⁺ → Cr³⁺ + Mn⁴⁺), enhancing the redox capacity of catalysts. According to the in situ diffuse reflectance infrared transform spectroscopy spectra, it could be concluded that the MnCr₂O₄-S-700 catalyst followed not only the Langmuir-Hinshelwood mechanism but also the Eley-Rideal mechanism. This work displays the effect of the complexation mechanism of chelating agents on the SCR reaction with NH₃ over spinel catalysts.