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- Mihai, Oana, 1975, et al.
(författare)
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The Effect of NO2/NOx Feed Ratio on the NH3-SCR System Over Cu–Zeolites with Varying Copper Loading
- 2014
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Ingår i: Catalysis Letters. - : Springer Science and Business Media LLC. - 1572-879X .- 1011-372X. ; 144:1, s. 70-80
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Tidskriftsartikel (refereegranskat)abstract
- In this study we examine the NO/NO2–NH3-SCR system over Cu–BEA with varying Cu loading. Significantly higher selective catalytic reduction (SCR) activity is observed at low temperature on highly loaded copper samples, whereas the reverse trend is noticed at high temperature. The N2O formation is substantially increased over “over-exchanged” Cu sites, where Cu co-ordinate to one Al and charge-balanced with one OH-group. This is also the case for NO2 reaction with NH3 to produce NO. Using transient experiments the formation/decomposition of ammonium nitrate species are examined. The decomposition depends on the temperature, the sequence of the feed as well as the type of copper species present.
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| 3. |
- Nedyalkova, Radka, 1976, et al.
(författare)
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Experimental evidence of the mechanism behind NH3 overconsumption during SCR over Fe-zeolites
- 2013
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Ingår i: Journal of Catalysis. - : Elsevier BV. - 0021-9517 .- 1090-2694. ; 299, s. 101-108
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Tidskriftsartikel (refereegranskat)abstract
- Isotope labeled (NO)-N-15 was used to investigate the mechanism of the unusual overconsumption of NH3 during standard SCR over Fe-zeolite, under conditions during which NH3 oxidation with O-2 alone (without NO) was unfavorable. When the Fe-BEA catalyst was exposed to the (NO)-N-15 + (NH3)-N-14 + O-2 gas mixture at 250 and 300 degrees C, the resulting products included (NO)-N-14, a product of (NH3)-N-14 oxidation under SCR conditions. However, (NO)-N-14 was not detected when Fe-BEA was exposed to (NH3)-N-14 + O-2. Since the only source of N-14 derives from (NH3)-N-14, with the labeled gas mixture used, the (NO)-N-14 during SCR must have originated from oxidation of (NH3)-N-14. Furthermore, twice as much (NN)-N-14-N-14 was observed at 300 degrees C under SCR conditions in comparison with NH3 oxidation using O-2 alone. Under SCR conditions, the (NO)-N-14 formed through the unusual oxidation route further reacted with (NH3)-N-14 to produce N-14(2). Thus, for the first time, we have experimental evidence for the unusual overconsumption of ammonia during SCR over Fe-zeolites.
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