Selective Catalytic Reduction of NOx with NH3 over Mn, Ce Substitution Ti0.9V0.1O2-δ Nanocomposites Catalysts Prepared by Self-Propagating High-Temperature Synthesis Method

This study focuses on promoting the low temperature performance of vanadium-based catalysts; for this, the SHS method was applied to synthesize a series of Ti0.9VxM0.1-xO2-delta catalysts. The performances of the catalysts (Ti0.9V0.1O2-delta, Ti0.9Mn0.05V0.05O2-delta, and Ti0.9Ce0.05V0.05O2-delta), were fully investigated with the temperature-programmed-reaction, which proved that these SHS catalysts with nanometer size had high activity over a broad temperature window of 150-400 degrees C. Compared with Ti0.9V0.1O2-delta, the substituted Catalysts, Ti0.9Mn0.05V0.05O2-delta and Ti0.9Ce0.05V0.05O2-delta, showed higher N-2 selectivity at high temperatures. The Ce substituted catalyst exhibited good resistance to H2O and SO2 poisoning at low temperatures. The structural and physical-chemical properties of catalysts were characterized comprehensively by BET, XRD, FTIR, TEM, EDX, XPS, and TPD. The XRD results indicated that the active components of V, Mn, and Ce were highly dispersed over the catalysts. The Mn substitution could enhance the Bronsted acid sites on the catalyst surface and accelerate the SCR reaction at low temperatures. The XPS shows that the Ce substitution led to high concentration of chemisorbed oxygen, which diminished the unselective oxidation of NH3 by O-2 to N2O, NO, or NO2 and resulted in superior N-2 selectivity. The active components of the catalysts, such as V, Mn, and Ce, mostly existed in the form of mixed-valence which was beneficial for the oxidation of NO to NO2. Furthermore, the SCR reaction mechanism over Ti0.9Ce0.05V0.05O2-delta catalyst was also examined using in situ DRIFTS. The results revealed that high active monodentate,e nitrate and bridging nitrate species as well as abundant ionic NH4+ (Bronsted acid sites) were the key intermediates in the SCR reaction since the ad-monodentate nitrate and bridging nitrate species disappeared quickly in the presence of NH3.