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 NO with NH3, Ti0.9Mn0.05Fe0.05O2-delta catalyst was prepared by self-propagating high-temperature synthesis (SHS) method and evaluated at 25-450 degrees C. The catalyst was characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The possible SCR mechanism over Ti0.9Mn0.05Fe0.05O2-delta was studied by in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). Ti0.9Mn0.05Fe0.05O2-delta showed both high SCR activity and N-2 selectivity over a broad temperature window of 100-350 degrees 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 Bronsted 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-delta. Additionally, the presence of O-2 significantly affects NO oxidation and coordinated NH3 activation. (c) 2014, Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier B.V. All rights reserved.