Characterization of copper species over Cu/SAPO-34 in selective catalytic reduction of NO x with ammonia: Relationships between active Cu sites and de-NO x performance at low temperature

Xue, Jinbo; Wang, Xinquan; Qi, Gongshin; Wang, Jun; Shen, Meiqing; Li, Wei

doi:10.1016/j.jcat.2012.09.020

Cited by 375 publications

(277 citation statements)

References 65 publications

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“…However, only the Cu ions located in or close to the 6-rings seem to contribute to the SCR activity in Cu-CHA. 12,[45][46][47][48] Independent of the nature and structure of the catalyst, and the local environment of the active sites, the SCR reaction can be divided in a reduction part and an oxidation part, quite similar to the well known Mars-Van Krevelen scheme for oxidation reactions. The reduction part corresponds to the steps in which the ammonia reacts with the NO to nitrogen and the catalytic site is reduced.…”

Section: Mechanistic Aspects Of the Scr Reactionmentioning

confidence: 99%

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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%

“…This is consistent with a constant activity per Cu atom. 47 Nevertheless, the formation of Cu dimers can still be beneficial for the SCR reaction. Measurements actually…”

Section: Role Of Cu-dimers and Brønsted Sitesmentioning

confidence: 99%

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

et al. 2015

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“…Such knowledge of the reaction mechanisms is essential for the development of kinetic models. While some investigations of the behaviour of Cu/SAPO-34 as a function of Cu loading have been published [20,21], there are still many mechanistic questions remaining. Furthermore, no kinetic models of SCR over Cu/SAPO-34 appear to have been published, so more mechanistic studies are of interest.…”

Section: Characterisation By X-ray Diffraction (Xrd)mentioning

confidence: 99%

Impact of Copper Loading on NH3-Selective Catalytic Reduction, Oxidation Reactions and N2O Formation over Cu/SAPO-34

et al. 2017

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Abstract:We developed a procedure for aqueous ion exchange to obtain different Cu loadings of Cu/SAPO-34 (between 0 and 2.6 wt %). The catalysts were washcoated on monoliths and characterised with respect to their activity and selectivity under standard selective catalytic reduction (SCR), fast SCR, NH 3 oxidation and NO oxidation reactions. They were further characterised using X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET), H 2 -temperature programmed reduction (H 2 -TPR), ultraviolet (UV)-vis spectroscopy and NH 3 adsorption. As expected, activity of all reactions increased with copper loading, due to increased number of active sites. However, the N 2 O formation during standard and fast SCR yielded interesting mechanistic information. We observed that N 2 O formation at low temperature increased with copper loading for the standard SCR reaction, while it decreased for fast SCR. The low-temperature N 2 O formation during fast SCR thus occurs predominantly over Brønsted sites. Species responsible for N 2 O formation during standard SCR, on the other hand, are formed on the copper sites. We further found that the fast SCR reaction occurs to a significant extent even over the H/SAPO-34 form. The Brønsted sites in SAPO-34 are thus active for the fast SCR reaction.

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“…It showed that the ratio of Cu 2+ to total copper loadings increased from 52 to 64% for the fresh CuCe 0.06 -SAPO-34 and Cu-SAPO-34 sample. This suggested that the addition of Ce to Cu-SAPO-34 could increase the amount of isolated Cu 2+ ions which are active sites for SCR reaction at low temperatures [21,22], resulting in the observed increase of SCR activity below 350°C. Similar results were reported by Y. Cao et al [15], that the interaction between cerium and copper could improve the dispersion of copper species and increase the amount of isolated Cu 2+ ions.…”

Section: H 2 -Tprmentioning

confidence: 99%

A novel one-pot synthesized CuCe-SAPO-34 catalyst with high NH3-SCR activity and H2O resistance

Niu

Shi

et al. 2016

Catalysis Communications

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CuCe-SAPO-34 catalysts based on the one-pot hydrothermal synthesis method were prepared for the first time. The addition of Ce suppressed the formation of CuO and increased the amount of active Cu 2+ , resulting in better NH 3 -SCR activity than Cu-SAPO-34. Ce greatly improved the H 2 O resistance during the SCR process by stabilizing the zeolite structure and obstructing the transformation of active Cu 2+ into inactive forms.

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Characterization of copper species over Cu/SAPO-34 in selective catalytic reduction of NO x with ammonia: Relationships between active Cu sites and de-NO x performance at low temperature

Cited by 375 publications

References 65 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

Impact of Copper Loading on NH3-Selective Catalytic Reduction, Oxidation Reactions and N2O Formation over Cu/SAPO-34

A novel one-pot synthesized CuCe-SAPO-34 catalyst with high NH3-SCR activity and H2O resistance

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