| 1. |
|
|
| 2. |
- Tamm, Stefanie, 1975, et al.
(författare)
-
Differences Between Al2O3 and Ag/Al2O3 for Lean Reduction of NOx with Dimethyl Ether
- 2009
-
Ingår i: Topics in Catalysis. - : Springer Science and Business Media LLC. - 1572-9028 .- 1022-5528. ; 52:13-20, s. 1813-1816
-
Tidskriftsartikel (refereegranskat)abstract
- Lean reduction of NOx with DME occurs with high selectivity to N-2 over Al2O3 between 300 degrees C and 550 degrees C with a maximum of 47% at 380 degrees C, and with lower selectivity over Ag/Al2O3 between 250 degrees C and 400 degrees C due to the catalysts' sensitivity to gas phase radical reactions and activity for NOx reduction with methanol.
|
|
| 3. |
|
|
| 4. |
- Tamm, Stefanie, 1975, et al.
(författare)
-
DME as reductant for continuous Lean Reduction of NOx over ZSM-5 Catalysts
- 2008
-
Ingår i: Catalysis Letters. - : Springer Science and Business Media LLC. - 1572-879X .- 1011-372X. ; 123:3-4, s. 233-238
-
Tidskriftsartikel (refereegranskat)abstract
- Dimethyl ether (DME) is an interesting alternativefuel to diesel, but is not an efficient reductant inlean NOx conversion over typical diesel HC-SCR catalysts.Comparatively high deNOx activity was found overH-ZSM-5 in the presence of water, giving reduction of28% NO and 37% NO2 respectively with a DME/NOxratioof 4.
|
|
| 5. |
|
|
| 6. |
- Tamm, Stefanie, 1975, et al.
(författare)
-
Influence of Gas Phase Reactions on DME-SCR over gamma-alumina
- 2011
-
Ingår i: Catalysis Letters. - : Springer Science and Business Media LLC. - 1572-879X .- 1011-372X. ; 141:5, s. 656-664
-
Tidskriftsartikel (refereegranskat)abstract
- Above 300 A degrees C, gas phase reactions occur between dimethyl ether (DME), NO and O-2 generating NO2. The influence of these reactions on DME-SCR was studied in a setup that decoupled the occurrence of gas phase reactions from catalyst temperature. NOx conversion decreased at 350 A degrees C and increased at 250 A degrees C due to less DME available and higher NCO conversion with NO2, respectively.
|
|
| 7. |
- Tamm, Stefanie, 1975, et al.
(författare)
-
Mechanistic aspects of the selective catalytic reduction of NOx by dimethyl ether and methanol over gamma-alumina
- 2010
-
Ingår i: Journal of Catalysis. - : Elsevier BV. - 0021-9517 .- 1090-2694. ; 276:2, s. 402-411
-
Tidskriftsartikel (refereegranskat)abstract
- High catalytic activity for selective catalytic reduction of NOx with dimethyl ether and methanol (DME- and methanol-SCR) has been found over a γ-alumina catalyst. The surface species involved in the DME-SCR reaction were studied by diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) in combination with mass spectrometry and compared to the corresponding species observed during methanol-SCR. Dimethyl ether adsorbs mainly as methoxy groups (OCH3) on the catalyst surface, while methanol adsorbs as methoxy groups and molecularly. With increasing temperature, DME desorbs in two steps, whereas methanol desorbs first as methanol and at higher temperatures as DME. At higher temperatures, the two reducing agents display similar DRIFTS spectra showing first formaldehyde-like species and then formates on the surface. In the presence of NO or NO2, reactions between NO x species and carbon-containing species occur. Formohydroxamic acid (CHON(H)OH) forms isocyanates (NCO), and both are observed at temperatures relevant for DME-SCR. Since these species are likely intermediates for hydrocarbon-SCR over Ag/Al2O3, a partly similar reaction mechanism may be operational for DME-SCR over γ-Al2O 3 despite the fact that Ag/Al2O3 does not catalyze DME-SCR efficiently. The difference is thus due to the reaction steps leading to the formation of formohydroxamic acid that with DME follow a more efficient route over γ-Al2O3 than over Ag/Al 2O3.© 2010 Elsevier Inc. All rights reserved.
|
|
| 8. |
- Tamm, Stefanie, 1975, et al.
(författare)
-
On the different roles of NCO and CN in propene-SCR over silver/alumina
- 2008
-
Ingår i: Journal of Catalysis. - : Elsevier BV. - 0021-9517 .- 1090-2694. ; 255:2, s. 304-312
-
Tidskriftsartikel (refereegranskat)abstract
- Silver/alumina is one of the most promising catalyst materials for HC-SCR. The reaction mechanism remains incompletely understood, however. Isocyanate species (–NCO) and cyanide species (–CN), important intermediates in the reaction path in HC-SCR, were investigated by gas-phase FTIR and DRIFT spectroscopy in step-response experiments. In accordance with the literature, the corresponding gas-phase species, HNCO and HCN, were always detected at the same time at the different steps of the experiment; however, the accumulation and consumption of surface –NCO and –CN species did not show a similar correlation. Consequently, in conflict with the literature, we propose two parallel, independent reaction pathways for –NCO and –CN species. In one of these reaction pathways, surface nitrates react with C-containing surface species either directly to –NCO or via R–NO2 species. In the other pathway, C-containing surface species react with gas-phase NOx or short-lived N-containing surface species to R–NO species and subsequently to –CN species.
|
|
| 9. |
|
|
| 10. |
- Tamm, Stefanie, 1975, et al.
(författare)
-
The influence of gas phase reactions on the design criteria for catalysts for lean NOx reduction with dimethyl ether
- 2009
-
Ingår i: Applied Catalysis B: Environmental. - : Elsevier BV. - 0926-3373 .- 1873-3883. ; 91:1-2, s. 234-241
-
Tidskriftsartikel (refereegranskat)abstract
- In the selective catalytic reduction (SCR) of NO by dimethyl ether (DME), the formation of unexpectedly high amounts of NO2 over 300 degrees C has previously been reported, In this study, we explain this phenomenon by radical reactions initiated by DME and O-2, during which DME is partly oxidized and NO2 is formed in the presence of NO. For the design criteria of a DME-SCR catalyst, these gas phase reactions have mainly three consequences: (i) another type of reducing agent than that fed into the reactor reaches the catalyst. (ii) no activation of the reducing agent such as partial oxidation is required, and (iii) several of the proposed intermediate species for HC-SCP, e.g. NO2, HONO, CH3-NO2, and CH3-NO form already in the gas phase. An efficient DME-SCR catalyst should thus have high selectivity for reduction of NO, predominately by partially oxidized Cl-compounds, and it should not have particularly strong oxidizing properties to avoid non-selective oxidation of these Cl-compounds. These two requirements appear to be reasonable well met by the acidic zeolite H-ZSM-5.
|
|
