Investigation of Two-Phase Intergrowth and Coexistence in Mn-Ce-Ti-O Catalysts for the Selective Catalytic Reduction of NO with NH3: Structure-Activity Relationship and Reaction Mechanism

TiO2-supported manganese catalysts have been widely investigated because of their unique catalytic properties. A series of Mn-Ce-Ti-O catalysts were synthesized by a modified sol-gel method. Mn atom doping into CT-0/1 samples results in anatase partly transforming into rutile and two-phase coexistence. X-ray photoelectron spectroscopy and NH3 temperature programmed desorption analysis show that the reactions of Mn3+ + Ti4+ <-> Mn4+ + Ti3+ and Ce4+ + Mn3+ <-> Ce3+ + Mn4+ happened, which is propitious to generating plentiful oxygen defects and chemical adsorbed oxygen and beneficial for the oxidation of NO to NO2. In addition, doping of Mn atoms could produce more acid sites and increase the ability of adsorption NH3 that reacted with NO2 to achieve high performance of deNO(x) in a wide temperature window. In situ diffusion reflectance infrared Fourier transform spectroscopy shows that MCT-15/1 achieves unpredictable NH3 selective catalytic reduction activity following transition from the Langmuir-Hinshelwood (L-H) mechanism to the Eley-Rideal (E-R) mechanism with rising temperature.