Effect of Oxygen Concentration in NH&lt;sub&gt;3&lt;/sub&gt;-SCR Reaction over Fe- and Cu-loaded Beta Zeolites

Takamitsu, Yasuyuki; Ito, Yuuki; Ogawa, Hiroshi; Sano, Tsuneji

doi:10.1627/jpi.55.57

Cited by 7 publications

(3 citation statements)

References 34 publications

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“…At the same temperature, NO conversion increased with the improvement of O 2 concentration. This is consistent with previous studies [35,36]. Noteworthy, the V-based catalyst still showed great applicability in the relatively oxygen-deficient flue gas, and 0.5% O 2 concentration was constant in the following in this research.…”

Section: Catalytic Studies Of V-w/ti Catalystssupporting

confidence: 92%

Applicability of V2O5-WO3/TiO2 Catalysts for the SCR Denitrification of Alumina Calcining Flue Gas

Ning

Chen

et al. 2019

Catalysts

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V2O5-WO3/TiO2 catalysts with different V2O5 and WO3 loadings were prepared by the impregnation method. H2O and SO2 resistance of the catalysts under high H2O concentration (30 vol.%) was studied. Influence of various basic metal oxides, such as Al2O3, CaO, Na2O, and K2O on the catalytic performance was studied and compared. It is revealed that the inhibitory effect is in the sequence of K > Na > Ca > Al, which is consistent with their alkalinity. X-ray diffraction (XRD), N2 physisorption (BET), temperature-programmed desorption of NH3 (NH3-TPD), H2-temperature programmed reduction (H2-TPR), X-ray photoelectron spectroscopy (XPS) and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) were carried out, and the results were well-correlated with the catalytic studies.

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Section: Catalytic Studies Of V-w/ti Catalystssupporting

confidence: 92%

Applicability of V2O5-WO3/TiO2 Catalysts for the SCR Denitrification of Alumina Calcining Flue Gas

Ning

Chen

et al. 2019

Catalysts

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“…Takamitsu et al observed similar results over a Cu-beta catalyst. 72 In contrast, the N 2 O yield gradually dropped from 45 to 4 ppm as the oxygen concentration was decreased from 14% to 0%, with no threshold within this range of O 2 concentration change.…”

Section: Energy and Fuelsmentioning

confidence: 91%

N₂O Formation Pathways over Zeolite-Supported Cu and Fe Catalysts in NH₃-SCR

2018

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N2O is a common byproduct in the NH3-SCR reaction. We analyzed the N2O formation pathways in NH3-SCR over various catalysts (Cu-ZSM-5, Fe-ZSM-5, Cu-SAPO-34, Fe-SAPO-34, Cu-SSZ-13, and Fe-SSZ-13), aided by catalyst characterization using XRD, XPS, EDS mapping, and NH3-TPD. The results showed that the NH3 nonselective catalytic reduction was the major N2O formation pathway for most of the Cu catalysts. The N2O formation at lower temperatures (<300 °C) originated mainly from decomposition of NH4NO3. In addition, NH3 nonselective oxidation was another reaction that formed N2O especially at higher temperatures. The N2O resulting from the Eley–Rideal mechanism was also favored at higher temperatures. The decomposition of NO to N2O and O2 also led to N2O formation, although its contribution was minimal. The absence of N2O yield over most Fe catalysts could be attributed to active N2O decomposition and N2O-SCR reactions. Moreover, varying O2 and H2O concentrations in the feed exerted strong influence on both N2O formation and SCR activity. Decrease in O2 level from 14% to 3% led to continual decline in N2O formation but had no effect on SCR activity until reaching a threshold concentration of 2%. H2O in lower concentrations (2–3%) facilitated N2O formation and NO conversion due to increase in Brønsted acidity, while H2O in higher concentrations (>5%) led to suppression of these reactions due to the coverage of active sites.

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“…First of all, the presence of NO 2 in the aftertreatment exhaust system is of commercial interest because sources of NO 2 upstream of the SCR unit originate from combustion in the engine and oxidation of NO to NO 2 by the diesel oxidation catalyst (DOC). The presence of NO 2 in the feed instigates the fast SCR pathway, , which unlike the standard SCR pathway is proposed to be a single-site reaction that occurs on both Cu 2+ and H + sites. ,,, In conjunction with all of these changes in the active centers, an increase in the NO 2 pressure is reported to increase N 2 O selectivity. ,− Although the presence of water between 0 and 12% does not significantly affect the standard SCR rate, , Tarach et al (Cu-ZSM-5 and Cu-TNU-9) and Zhang et al (Cu-ZSM-5, Cu-SAPO-34, Cu-SSZ-13) reported that an increase in water increases the N 2 O selectivity on Cu zeolites. At 523 K, Liu et al observed an increase in N 2 O selectivity with increasing H 2 O from 0 to 2% and a decrease in N 2 O selectivity at water concentrations greater than 2%.…”

Section: Introductionmentioning

confidence: 99%

Influence of ZCuOH, Z₂Cu, and Extraframework Cu_xO_y Species in Cu-SSZ-13 on N₂O Formation during the Selective Catalytic Reduction of NO_x with NH₃

et al. 2021

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In this contribution, we synthesized three model Cu-SSZ-13 catalysts with primarily ZCuOH, Z2Cu, and extraframework Cu x O y species and then measured their N2O formation rates during standard selective catalytic reduction (SCR). We first present evidence that the formation of extraframework Cu x O y species after sequential aqueous ion exchange and calcination correlates with the formation of Cu(OH)2 precipitates during ion exchange. These Cu x O y species are not active for standard SCR, and unchanged apparent activation energies and reaction orders demonstrate that these Cu x O y species do not induce transport limitations to accessible Cu2+ active centers. During standard SCR, N2O formation rates on a per Cu basis were the fastest (and exhibited higher selectivities) on ZCuOH, followed by Z2Cu and then extraframework Cu x O y . Because N2O formation apparent activation energies were indistinguishable from the standard SCR apparent activation energies associated with the reduction-limited step, we posit that N2O is formed during the standard SCR reduction step. Additionally, using sulfur poisons to force the ZCuOH rate-limiting step to the oxidation half-cycle resulted in an unchanged N2O formation apparent activation energy, further supporting our hypothesis. These results suggest that utilizing Cu-SSZ-13 catalysts with higher fractions of Z2Cu active centers in commercial aftertreatment systems can lead to reduced N2O emissions.

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Effect of Oxygen Concentration in NH<sub>3</sub>-SCR Reaction over Fe- and Cu-loaded Beta Zeolites

Cited by 7 publications

References 34 publications

Applicability of V2O5-WO3/TiO2 Catalysts for the SCR Denitrification of Alumina Calcining Flue Gas

Applicability of V2O5-WO3/TiO2 Catalysts for the SCR Denitrification of Alumina Calcining Flue Gas

N₂O Formation Pathways over Zeolite-Supported Cu and Fe Catalysts in NH₃-SCR

Influence of ZCuOH, Z₂Cu, and Extraframework Cu_xO_y Species in Cu-SSZ-13 on N₂O Formation during the Selective Catalytic Reduction of NO_x with NH₃

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Effect of Oxygen Concentration in NH<sub>3</sub>-SCR Reaction over Fe- and Cu-loaded Beta Zeolites

Cited by 7 publications

References 34 publications

Applicability of V2O5-WO3/TiO2 Catalysts for the SCR Denitrification of Alumina Calcining Flue Gas

Applicability of V2O5-WO3/TiO2 Catalysts for the SCR Denitrification of Alumina Calcining Flue Gas

N2O Formation Pathways over Zeolite-Supported Cu and Fe Catalysts in NH3-SCR

Influence of ZCuOH, Z2Cu, and Extraframework CuxOy Species in Cu-SSZ-13 on N2O Formation during the Selective Catalytic Reduction of NOx with NH3

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N₂O Formation Pathways over Zeolite-Supported Cu and Fe Catalysts in NH₃-SCR

Influence of ZCuOH, Z₂Cu, and Extraframework Cu_xO_y Species in Cu-SSZ-13 on N₂O Formation during the Selective Catalytic Reduction of NO_x with NH₃