Diesel Soot Catalyzes the Selective Catalytic Reduction of NOx with NH3

Abstract

The catalytic activity of soot samples for the selective catalytic reduction (SCR) of NO x with NH 3 was investigated in dependence of the NO 2 , NO and NH 3 concentration in the temperature range between 200 and 350°C. The highest NO x reduction of up to 25 % was measured in the presence of both NO 2 and NO at a GHSV of 35,000 h-1. Decreasing space velocities resulted in an increase of the SCR activity. In the absence of NO 2 , NO x reduction was not observed. Carbon oxidation and SCR reaction occurred in parallel due to the presence of NO 2 and O 2 , but hardly influenced each other, which suggested that in the NO x reduction on soot most probably physisorbed species were involved. The observed stoichiometries indicated the action of the fast SCR reaction in the presence of NO and the NO 2 SCR reaction in the absence of NO, while the observed gas phase and surface species pointed at reaction steps similar to those on classical SCR catalysts.

Inorganic Salt Interference on CO2+ in Aerodyne AMS and ACSM Organic Aerosol Composition Studies

“…Oxidation of organic carbonaceous residues to CO and CO 2 by HNO 3 and NO x is well-known in mass spectrometry research of NO 2 and HNO 3 . , Further, soot oxidation research and the automobile industry make use of carbon oxidation under high-NO x conditions. − , For instance, high NO x levels and enhanced temperatures in the vehicle exhaust are used to facilitate the regeneration of diesel particulate filters and to burn off carbonaceous deposits to CO 2 . (Elemental) carbon is also used as a catalyst for the catalytic reduction of NO x to N 2 with NH 3 . , It is likely that similar conditions drive the CO and CO 2 formation inside the ion chamber when NH 4 NO 3 or other nitrate salts decompose to HNO 3 and NO x (i.e., NO 2 and NO) on the 600 °C heated AMS and ACSM vaporizer. Also, the observed CO + -to-CO 2 + ratio (RIE = 1 for both species) of around 1 (note: EI impact CO + -to-CO 2 + ratio = 0.1) is in line with literature reports on soot oxidation with nitrogen oxides (0.2–1) .…”

“…For instance, high NO x levels and enhanced temperatures in the vehicle exhaust are used to facilitate regeneration of diesel particulate filters and to burn off carbonaceous deposits to CO 2 . On the other hand, (elemental) carbon is used as a catalyst for the selective catalytic reduction of NO x to N 2 [33][34][35]. Likely, similar conditions drive the CO and CO 2 formation inside the ion chamber, whenNH 4 NO 3 or other nitrate salts decompose to HNO 3 , NO 2 and NO (NO x ) on the 600 °C heated AMS/ACSM vaporizer.…”

Site-selectively grown SnO2 NWs networks on micromembranes for efficient ammonia sensing in humid conditions

“…4 (c), the labelled region III. The variation in transient behavior at 450 °C suggests that a different reaction takes place, which could correspond to reaction (5), since this latter starts to dominate at about 400 °C. The temperature intervals for NO reaction are in agreement with other works, and are also supported by the transient decay of the sensor resistance at 400 and 450 °C.…”

“…and (5) in the steady sensing state. Furthermore, 60% of relative humidity at 20 °C corresponds to approximately 14300 ppm of water, a concentration 3 orders of magnitude higher than ammonia in these experiments.…”

“…Furthermore, ammonia, together with urea, is used in automotive applications for selective catalytic reduction (SCR) of nitrogen oxide (NOx) to nitrogen in order to avoid harmful gas emissions in diesel heavy weight engines, which gives also H2O as a byproduct [4,5]. Accurate measurements of the ammonia concentration for SCR are needed for an efficient process and the recycling of the non-reacted ammonia fraction.…”