Mechanism of N₂O Formation during the Low-Temperature Selective Catalytic Reduction of NO with NH₃ over Mn–Fe Spinel

Abstract

The mechanism of N2O formation during the low-temperature selective catalytic reduction reaction (SCR) over Mn-Fe spinel was studied. The in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and transient reaction studies demonstrated that the Eley-Rideal mechanism (i.e., the reaction of adsorbed NH3 species with gaseous NO) and the Langmuir-Hinshelwood mechanism (i.e., the reaction of adsorbed NH3 species with adsorbed NOx species) both contributed to N2O formation. However, N2O selectivity of NO reduction over Mn-Fe spinel through the Langmuir-Hinshelwood mechanism was much less than that through the Eley-Rideal mechanism. The ratio of NO reduction over Mn-Fe spinel through the Langmuir-Hinshelwood mechanism remarkably increased; therefore, N2O selectivity of NO reduction over Mn-Fe spinel decreased with the decrease of the gas hourly space velocity (GHSV). As the gaseous NH3 concentration increased, N2O selectivity of NO reduction over Mn-Fe spinel increased because of the promotion of NO reduction through the Eley-Rideal mechanism. Meanwhile, N2O selectivity of NO reduction over Mn-Fe spinel decreased with the increase of the gaseous NO concentration because the formation of NH on Mn-Fe spinel was restrained. Therefore, N2O selectivity of NO reduction over Mn-Fe spinel was related to the GHSV and concentrations of reactants.

Investigations on the Antimony Promotional Effect on CeO2–WO3/TiO2 for Selective Catalytic Reduction of NOx with NH3

“…It has been reported that manganese-doped CeO 2 -WO 3 catalyst improves the de-NO x activity at lower temperature, whereas its poor selectivity toward N 2 restrains its employment. [27,28] Peng Antimony-doped CeO 2 -WO 3 /TiO 2 catalysts were prepared by a conventional ultrasonic-assisted impregnation method and employed for selective catalytic reduction of NO x with NH 3 at low temperature. Both experimental work and theoretical studies were employed to elucidate the effect of the antimony on promoting the CeO 2 -WO 3 /TiO 2 catalyst.…”

High N2 selectivity in selective catalytic reduction of NO with NH3 over Mn/Ti–Zr catalysts

“…It has been previously reported that Lewis acid sites are benecial to NO conversion, which agreed with the result of activity measurements. 37 Besides, the Brønsted acid sites are advantage for the adsorption of NH 3 . 38 In fact, although gaseous NH 3 could be adsorbed on both Lewis acid sites and Brønsted acid sites during the SCR process, it was the Lewis acid sites that mainly exerted a positive effect.…”

Experimental Research of an Active Solution for Modeling In Situ Activating Selective Catalytic Reduction Catalyst

“…The Lewis acid site formed by Mo 6+ can enhance the acidity of the catalyst surface and strengthen the adsorption process of NH 3 on the catalyst surface. Previous studies [30,31] have shown that Mo could promote the dispersion of VO x species on the surface of TiO 2 . Importantly, V and W have a synergistic effect [32].…”

“…There are numerous possible reasons for this observation. Firstly, the depletion of the active ingredient (V2O5) could be the cause, the vanadium oxide could have been disseminated on the catalyst in an amorphous or highly dispersed form (Figure 8), or the molybdenum improved the dispersion of monolayer VOx species on TiO2 and the tungsten on the catalyst surface suppressed the progressive transformation of monomeric vanadyl species into crystalline V2O5 [31,47]. At the same time, the diffraction peak of WO3 appeared in the sample, but the diffraction peaks of WO3 did not appear, indicating that the dispersion of WO3 was slightly less, and WO3 did not sufficiently contact TiO2.…”