Chemisorption of NO₂ on V-Based SCR Catalysts: A Fundamental Study toward the Mechanism of “Fast SCR” Reaction

Abstract

The "fast selective catalytic reduction (SCR)" process, with its superior efficiency, is promising for removing NO x from flue gas with low temperature and high gas velocity. Chemisorption of NO 2 is a crucial step in this heterogeneous catalysis process. In this study, density functional theory calculations and experimental methods were implemented to study the chemisorption behaviors of NO 2 on the industrial V-based SCR catalyst. Both the ( 001) and ( 101) surfaces of the TiO 2 support were applied in the modeling and calculation process. Theoretical results show varied profiles of NO 2 adsorption on the fresh and reduced V 2 O 5 /TiO 2 catalysts. For the fresh catalyst, NO 2 tends to adsorb on the TiO 2 support rather than on the vanadium oxide. On the contrary, NO 2 exhibits a strong interaction with the −OH site of the reduced vanadium oxide. NO 2 temperature-programmed desorption, X-ray photoelectron spectroscopy, and a designed redox experiment were implemented to verify the calculation results. On the basis of the NO 2 adsorption behaviors, we concluded two different reaction mechanisms of the "fast SCR" reaction. One is that NO 2 significantly accelerates the reoxidation process of the reduced vanadia sites and the other is that the adsorbed NO 2 on TiO 2 reacts with NH 3 and NO in the path of the "Nitrate route" with the assistance of an adjacent vanadia site.

Computational Design of Gas Sensors Based on V3S4 Monolayer

“…This led to elongation of one of the N–O bonds to 1.42 Å. Such a feature indicates not only sensoric applications of V 3 S 4 , but can also be useful for the catalytic reduction of NO 2 [ 60 ].…”

Recycling of Waste SCR Catalysts Using a Catalytic Filter: A Study on the Catalytic Performance for NOx Abatement

“…Therefore, the active sites were covered and the catalyst was deactivated. However, surface NH 4 + of NH 4 HSO 4 can rapidly react with the NO/NO 2 /O 2 mixture under Fast SCR conditions, which will promote the decomposition of deposited NH 4 HSO 4 on the catalyst. − After SO 2 injection, the activity of the catalytic filter recovered, which was only 2% lower than that before SO 2 injection, exhibiting excellent sulfur resistance.…”

“…In earlier studies, our research team has done much research on the reaction of ammonium bisulfate on a vanadia SCR catalyst. The results show that the presence of NO 2 can accelerate the decomposition of NH 4 HSO 4 deposited on the surface of the catalyst. − In addition, the equimolar NO/NO 2 reaction was defined as the “Fast SCR”, because the reaction rate of the Fast SCR is more than 10 times faster than that of the standard SCR . Therefore, sulfur resistance of the catalyst is greatly enhanced in the reaction atmosphere of Fast SCR due to the dynamic balance between deposition and decomposition.…”

Effect of Calcination Temperature on the Activation Performance and Reaction Mechanism of Ce–Mn–Ru/TiO2 Catalysts for Selective Catalytic Reduction of NO with NH3

“…It can be confirmed that the mechanism of CMRT-X catalysts is not fast SCR. 54 Moreover, adsorption of NO + O 2 on the surface of three CMRT catalysts resulted in the formation of eight NO active species: bridged nitrate (1250 and 1606 cm –1 ), 17 monodentate nitrates (1286 and 1488, cm –1 ), 17 , 45 M n + -NO 2 species (1315–1350 cm –1 ), 55 − 57 unstable N 2 O 4 species (1521 and 1522 cm –1 ), 58 ionic nitrates (1457 and 1473 cm –1 ), 49 , 59 bidentate nitrates (1506, 1540, 1555, 1558, and 1583 cm –1 ), 14 , 59 , 60 Ru n + -NO molecules (1890 cm –1 ), 49 , 61 − 63 M n + -H 2 O (1715–1866 cm –1 ), and adsorbed NO species (1158 cm –1 ) ( Figure 5 b–d). 17 These results suggest that the CMRT-350 catalyst adsorbs most types and amount of NO active species, indicating that the reaction between NO and O 2 is most active on the surface of CMRT-350.…”