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 Ti 0.9 V x M 0.1– x O 2−δ catalysts. The performances of the catalysts (Ti 0.9 V 0.1 O 2−δ, Ti 0.9 Mn 0.05 V 0.05 O 2−δ, and Ti 0.9 Ce 0.05 V 0.05 O 2−δ ) 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 °C. Compared with Ti 0.9 V 0.1 O 2−δ, the substituted catalysts, Ti 0.9 Mn 0.05 V 0.05 O 2−δ and Ti 0.9 Ce 0.05 V 0.05 O 2−δ, showed higher N 2 selectivity at high temperatures. The Ce substituted catalyst exhibited good resistance to H 2 O and SO 2 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 Brønsted 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 NH 3 by O 2 to N 2 O, NO, or NO 2 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 NO 2 . Furthermore, the SCR reaction mechanism over Ti 0.9 Ce 0.05 V 0.05 O 2−δ catalyst was also examined using in situ DRIFTS. The results revealed that high active monodentate nitrate and bridging nitrate species as well as abundant ionic NH 4 + (Brønsted 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 NH 3 .