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Selective catalytic reduction of NO

Ammonia leakage from the aftertreatment of diesel vehicles arouses serious environmental concerns, thus demanding a high-efficiency ammonia elimination catalyst. In the present work, the mechanism ...

The mechanism of H2-assisted NH3-selective catalytic reduction (SCR) over Ag/Al2O3 was systematically investigated by kinetic measurements and in situ diffuse reflectance infrared Fourier transform...

Adsorption is an efficient method for atmospheric NOx abatement under ambient conditions; however, traditional adsorbents suffer from limited adsorption capacity and byproduct formation. Developing a low-cost material with high capacity for atmospheric NO2 elimination remains a challenge. Here, we synthesized a nanodispersed Mn3O4/γ-Al2O3 (Mn/Al) material that exhibits excellent ability to remove NO2. The 10 wt % Mn/Al sample showed the highest removal capacity, with 247.6 mgNO2/gMn/Al, which is superior to that of activated carbon (42.6 mgNO2/g). There were no byproducts produced when Mn/Al was tested with ppb-level NO2. The NO2 abatement mechanism with Mn/Al is different from physisorption or chemisorption. NO2 removal is mainly a catalytic process in air, during which surface hydroxyls and lattice oxygen are involved in the oxidation of NO2 to nitrate. In contrast, a chemical reaction between Mn3+ and NO2 is dominant in N2, where Mn3+ is converted into Mn4+ and NO2 is reduced to nitrite. Washing with deionized water is an effective and convenient method for the regeneration of saturated Mn/Al, and an 86% adsorption capacity was recovered after one washing. The results suggest that this low-cost Mn/Al material with easy preparation and regeneration is a promising candidate material for atmospheric NO2 elimination.

Ag-based catalysts are efficient materials for formaldehyde (HCHO) oxidation in the low-temperature range. It has been reported that K addition can increase the catalytic performance of Ag-based catalysts, whereas the specific role of K doping remains ambiguous. In this work, Ag/Al2O3 and K–Ag/Al2O3 catalysts with different K doping levels were prepared and subsequently tested for catalytic HCHO oxidation. It was observed that K doping has a dramatic promotion effect on the activity of the Ag/Al2O3 catalyst. The 2K–Ag/Al2O3 sample was the most active catalyst, over which HCHO could be completely converted into CO2 and H2O in a gas hourly space velocity of 100 000 mL/(gcat h) at 65 °C. The catalysts were next characterized by X-ray powder diffraction, Brunauer–Emmett–Teller, transmission electron microscopy, H2-temperature-programmed reduction, UV–vis, X-ray absorption fine structure, and in situ diffuse reflectance infrared Fourier transform spectroscopy methods. The characterization results show that add...

A negative temperature dependence was found for the selective catalytic reduction of NOx by ethanol (ethanol-SCR) over Ag/Al2O3 in the absence of water vapor. Activation energy measurements for this process confirmed that two reaction routes occurred in different temperature ranges. In situ DRIFTS experiments revealed that these temperature-dependent reactions were closely related to the process of the partial oxidation of ethanol. During the partial oxidation of ethanol at low temperatures below 400 °C, enolic species and acetates were produced, the former of which exhibited much higher activity for NOx reduction than the latter. Therefore, the formation of enolic species and their further transformation to produce N2 governs the low-temperature route for ethanol-SCR. At temperatures above 400 °C, only acetate appeared during the partial oxidation of ethanol, and its further reaction with NOx accounts for the high-temperature route. More importantly, introduction of water vapor significantly enhanced the...

The influence of the silver valence state on Ag/Al2O3 on the water tolerance of H2-C3H6-SCR of NOx was investigated. The valence state of silver species on Ag/Al2O3, which was carefully characterized by XPS, UV-vis, and XANES measurements, was adjusted by varying the calcination temperature from 500 oC to 900 oC. Oxidized silver species were predominant on Ag/Al2O3 calcined at temperatures below 600 oC (LT-catalysts), while further increasing the calcination (temperatures above 600 oC, HT-catalysts) promoted the transformation of oxidized silver species into metallic silver clusters. The samples with higher amounts of oxidized silver species exhibited better water tolerance in the H2-C3H6-SCR. Activation energy measurements confirmed that the mechanism of NOx reduction on these catalysts was the same. In situ DRIFTS studies demonstrated that metallic silver species promoted the formation of active enolic species and the complete oxidation of formate, thus improving the low-temperature activity of HT-catal...