In situ DRIFTS study of the mechanism of low temperature selective catalytic reduction over manganese-iron oxides

To investigate the mechanism of selective catalytic reduction (SCR) of NOx with NH3, Ti0.9Mn0.05Fe0.05O2-δ catalyst was prepared by self-propagating high-temperature synthesis (SHS) method and evaluated at 25–450 °C. The catalyst was characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The possible SCR mechanism over Ti0.9Mn0.05Fe0.05O2-δ was studied by in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). Ti0.9Mn0.05Fe0.05O2-δ showed both high SCR activity and N2 selectivity over a broad temperature window of 100–350 °C. The XRD and TEM results indicated that the active components of Mn and Fe were in a highly dispersed state and in an amorphous form on TiO2. The DRIFTS results revealed that Brönsted acid sites were the active centers for NO removal and monodentate nitrates were the key intermediate in the SCR reaction. At 150 °C, both Langmuir-Hinshelwood and Eley-Rideal mechanisms are involved in the SCR reaction, while the former one mechanism dominates the catalytic activity of Ti0.9Mn0.05Fe0.05O2-δ. Additionally, the presence of O2 significantly affects NO oxidation and coordinated NH3 activation.

Graphical AbstractSelective catalytic reduction reactions over Ti0.9Mn0.05Fe0.05O2-δ catalysts possibly proceed according to both Langmuir-Hinshelwood and Eley-Rideal mechanisms, but NO more likely reacts as an adsorbed species.Figure optionsDownload as PowerPoint slide