A comparative study of the NH3-SCR reactions over a Cu-zeolite and a Fe-zeolite catalyst

Colombo, Massimo; Nova, Isabella; Tronconi, Enrico

doi:10.1016/j.cattod.2010.01.010

Cited by 278 publications

(188 citation statements)

References 38 publications

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“…In the presence of excess NO 2 , like for the conditions of Fig. 8, apparently the NO 2 -activated soot combustion, reactions R.3 and R.4, can compete to some extent with the NH 3 -SCR reactions: this results in converting a certain amount of NO 2 to NO, which shifts the actual NO 2 /NO x ratio from the original unit value to a more favorable value closer to the optimal 0.5 ratio of the fast SCR reaction [12], thus boosting the overall deNO x performances and lowering the N 2 O selectivity.…”

Section: Effect Of Nh 3 + No X On Soot Combustionmentioning

confidence: 88%

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Interaction of NO x Reduction and Soot Oxidation in a DPF with Cu-Zeolite SCR Coating

Tronconi

Nova

Marchitti

et al. 2015

Emiss. Control Sci. Technol.

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The combination of selective catalytic reduction (SCR) and diesel particulate filter (DPF) in one system (so called SDPF) enables a very compact design and has already found its way into commercial application for passenger cars. In the case of heavy-duty and non-road applications, the design and control of the SDPF heavily depends on the interaction between NO x reduction and soot oxidation reactions taking place in close vicinity. The governing phenomena are described and studied in the present work by means of multi-scale experimental testing and mathematical modeling. Detailed kinetic studies at a micro-scale laboratory test rig are used to acquire the intrinsic reaction rates of the NH 3 -SCR reactions over a Cu-based catalyst, as well as to obtain qualitative trends of the role of soot presence. The above reaction kinetics are then directly implemented in a physicochemical model of the transport and reaction processes in a wall-flowcatalyzed filter. This model is validated against medium-scale engine tests revealing the competitive effects of SCR and passive soot oxidation, by a simple superposition of SCR chemistry and soot oxidation chemistry. This indicates that proper modeling of the species diffusion processes in the channels, the soot layer, and the wall is sufficient to describe the inhibiting effect of NH 3 -SCR on soot oxidation. This allows for a straightforward decoupled model calibration process which can be used to develop efficient system design and dosing control methodologies. Finally, the model is applied to a much different SDPF scale relevant for large non-road engines. The necessary adaptations to the model parameters are discussed as well as a methodology to apply predictive simulation tools when the boundary conditions are changed.

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Section: Effect Of Nh 3 + No X On Soot Combustionmentioning

confidence: 88%

“…Considering that the literature model had been originally developed for a Fe-zeolite catalyst, it was necessary to modify it in order to comply with the typical, slightly different behavior of Cu-zeolite catalysts [12] as follows:…”

Section: Nh 3 -Scr Kinetic Modelmentioning

confidence: 99%

Interaction of NO x Reduction and Soot Oxidation in a DPF with Cu-Zeolite SCR Coating

Tronconi

Nova

Marchitti

et al. 2015

Emiss. Control Sci. Technol.

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“…This is an indication that this reaction step is an equilibrium reaction, which is consistent with earlier reports that this reaction can occur in both directions. 55,62,63 As noted above, the rate determining step of the standard SCR reaction is the oxidation of NO to nitrates (step 1) or the release of NO 2 (step 2). The calculated activation energies for these steps are 1.08 eV for the nitrate formation, and 0.67 eV for the release of NO 2 ( Figure 3).…”

Section: Verification Of the Reaction Schemementioning

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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“…Rahkamaa-Tolonen et al have investigated the NH3-SCR of NO over a number of transition metal ion-exchanged beta zeolite catalysts and found that the catalytic activity at temperatures lower than 400 decreased as follows: Fe Cu Ag H. The loaded metal species served as the active component for catalysing the oxidation of NO to NO2 1) . Colombo et al have reported notable differences in the NH3 effect on the NH3-SCR activity between Fe-and Cu-loaded beta zeolite catalysts, namely a negligible effect of NH3 on the Cu-loaded zeolite and a severe inhibitory effect of NH3 on the Fe-loaded zeolite 2) . Fedeyko et al have reported an investigation into the adsorption behaviour of NOx and NH3 over Fe-and Cu-loaded beta zeolites by means of an FT-IR technique.…”

Section: Introductionmentioning

confidence: 99%

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

Takamitsu

Ito

Ogawa

et al. 2012

J. Jpn. Petrol. Inst.

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A comparative study of the NH3-SCR reactions over a Cu-zeolite and a Fe-zeolite catalyst

Cited by 278 publications

References 38 publications

Interaction of NO x Reduction and Soot Oxidation in a DPF with Cu-Zeolite SCR Coating

Interaction of NO x Reduction and Soot Oxidation in a DPF with Cu-Zeolite SCR Coating

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

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

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