Selective catalytic reduction of NOx with NH3 over zeolite H–ZSM-5: influence of transient ammonia supply

Wallin, Mikaela

doi:10.1016/s0021-9517(03)00148-9

Cited by 102 publications

(30 citation statements)

References 18 publications

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“…15 Based on the fact that the SCR reaction becomes much faster in the presence of NO 2 , this step has also been proposed as the rate determining step for the standard SCR reaction. [56][57][58][59] The adsorbed NO 2 is the first step in the formation of reactive nitrate and nitrite species, 15,40 which could occur by disproportionation of two NO 2 molecules to 8 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 NO an isolated negative charge on the catalyst, or the second oxygen atom in 1 2 O 2 must be accommodated in the catalyst. These changes have to be restored as well in order to close the catalytic cycle.…”

Section: Mechanistic Aspects Of the Scr Reactionmentioning

confidence: 99%

A Consistent Reaction Scheme for the Selective Catalytic Reduction of Nitrogen Oxides with Ammonia

et al. 2015

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For the first time, the standard and fast selective catalytic reduction (SCR) of NO by NH3 are described in a complete catalytic cycle that is able to produce the correct stoichiometry while allowing adsorption and desorption of stable molecules only. The standard SCR reaction is a coupling of the activation of NO by O2 with the fast SCR reaction, enabled by the release of NO2. According to the scheme, the SCR reaction can be divided into an oxidation of the catalyst by NO + O2 and a reduction by NO + NH3; these steps together constitute a complete catalytic cycle. Furthermore, both NO and NH3 are required in the reduction, and finally, oxidation by NO + O2 or NO2 leads to the same state of the catalyst. These points are shown experimentally for a Cu-CHA catalyst by combining in situ X-ray absorption spectroscopy (XAS), electron paramagnetic resonance (EPR), and Fourier transform infrared spectroscopy (FTIR). A consequence of the reaction scheme is that all intermediates in fast SCR are also part of the standard SCR cycle. The activation energy calculated by density functional theory (DFT) indicates that the oxidation of an NO molecule by O2 to a bidentate nitrate ligand is rate-determining for standard SCR. Finally, the role of a nitrate/nitrite equilibrium and the possible influence of Cu dimers and Brønsted sites are discussed, and an explanation is offered as to how a catalyst can be effective for SCR while being a poor catalyst for NO oxidation to NO2.

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Section: Mechanistic Aspects Of the Scr Reactionmentioning

confidence: 99%

A Consistent Reaction Scheme for the Selective Catalytic Reduction of Nitrogen Oxides with Ammonia

et al. 2015

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“…2 Hence, different experimental and theoretical studies were focused on the effect of the metal (Cu, Fe, Ce, Co and Ag) and type of the zeolites (ZSM-5, MFI, FER, BEA, SSZ-13 and SAPO-34) 4,7-9 , on the stability and the overall SCR performance. 7,9,[10][11][12] In general, Fe-and Cu-based zeolites are selected as the most active SCR catalysts for NO x reduction. 13,14 In particular, it was found that the Cu-ion exchanged zeolites are characterized by superior low temperature activity.…”

Section: Usamentioning

confidence: 99%

The effect of iron loading and hydrothermal aging on one-pot synthesized Fe/SAPO-34 for ammonia SCR

Andonova

Tamm

Montreuil

et al. 2016

Applied Catalysis B: Environmental

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“…Although most of the research is currently focused on the study of zeolite‐based catalysts,2–13 traditional extruded SCR monoliths made of V 2 O 5 ‐WO 3 /TiO 2 catalysts are still used in Europe at a commercial scale. Extensive work was devoted in the past to study V 2 O 5 ‐WO 3 /TiO 2 catalysts for DeNO x ing of stack gases from power plants and other stationary sources14, 15: in such cases V‐based catalysts showed the best performances in the 300–400°C T ‐range where the Standard SCR reaction was active according to the stoichiometry However, moving from stationary to mobile applications, a wider T ‐window has to be addressed1: in particular, a greater activity in the low‐temperature region is required.…”

Section: Introductionmentioning

confidence: 99%

Unifying redox kinetics for standard and fast NH₃‐SCR over a V₂O₅‐WO₃/TiO₂ catalyst

et al. 2009

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in Wiley InterScience (www.interscience.wiley.com).A dynamic Mars-van Krevelen kinetic model that unifies Standard and Fast SCR reactions into a single redox approach is herein proposed for V-based catalysts for NO x removal from Diesel exhausts. Such a mechanistic model is consistent with the detailed catalytic chemistry proposed for the NH 3 -NO/NO 2 reacting system in which NO 2 disproportionates to form nitrites and nitrates, nitrates are reduced by NO to nitrites in a key redox step, and nitrites react with NH 3 to form N 2 via decomposition of unstable ammonium nitrite. Intrinsic kinetic parameters were estimated by global multiresponse nonlinear regression of 42 transient runs. The model accounts for stoichiometry, selectivity, and kinetics of the global SCR process, reproducing successfully both the steady-state and transient behaviors of the SCR reacting system over the full range (0-1) of NO 2 /NO x feed ratios in the 175-425 C temperature range. V U 2 ¼ 0:028 \ 0:08 Thus, also intraphase mass transfer limitations can be ruled out.

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Selective catalytic reduction of NOx with NH3 over zeolite H–ZSM-5: influence of transient ammonia supply

Cited by 102 publications

References 18 publications

A Consistent Reaction Scheme for the Selective Catalytic Reduction of Nitrogen Oxides with Ammonia

A Consistent Reaction Scheme for the Selective Catalytic Reduction of Nitrogen Oxides with Ammonia

The effect of iron loading and hydrothermal aging on one-pot synthesized Fe/SAPO-34 for ammonia SCR

Unifying redox kinetics for standard and fast NH₃‐SCR over a V₂O₅‐WO₃/TiO₂ catalyst

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Selective catalytic reduction of NOx with NH3 over zeolite H–ZSM-5: influence of transient ammonia supply

Cited by 102 publications

References 18 publications

A Consistent Reaction Scheme for the Selective Catalytic Reduction of Nitrogen Oxides with Ammonia

A Consistent Reaction Scheme for the Selective Catalytic Reduction of Nitrogen Oxides with Ammonia

The effect of iron loading and hydrothermal aging on one-pot synthesized Fe/SAPO-34 for ammonia SCR

Unifying redox kinetics for standard and fast NH3‐SCR over a V2O5‐WO3/TiO2 catalyst

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Unifying redox kinetics for standard and fast NH₃‐SCR over a V₂O₅‐WO₃/TiO₂ catalyst