The dynamic nature of Cu sites in Cu-SSZ-13 and the origin of the seagull NO<sub>x</sub> conversion profile during NH<sub>3</sub>-SCR

Fahami, A.R.; Günter, T.; Doronkin, Dmitry E.; Casapu, Maria; Zengel, Deniz; Vuong, Thanh Huyen; Simon, Michael A.; Breher, Frank; Кучеров, А. В.; Brückner, Angelika; Grunwaldt, Jan‐Dierk

doi:10.1039/c8re00290h

Cited by 83 publications

(102 citation statements)

References 73 publications

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“…Instead, an increasing proportion of Cu II −Z (purple) is observed suggesting that Cu is primarily interacting directly with the zeolite framework. The loss of coordinating ligands upon heating has also previously been observed elsewhere …”

Section: Resultssupporting

confidence: 56%

“…Furthermore, on addition of NO to the gas feed at 283 °C there is a continual rise in the Cu I −Z proportion. This suggests that the oxidation to Cu II −Z is limiting the SCR reaction in this temperature regime and may explain the dip in SCR activity typically observed between 250 and 350 °C, often denoted as a seagull shape …”

Section: Resultsmentioning

confidence: 98%

“…However, accurate standard compounds do not exist to describe the Cu‐species present when Cu is interacting directly with the zeolite framework. Recent studies have demonstrated the power of multivariate curve resolution (MCR) methods towards the determination of evolving spectral components in time‐resolved XANES datasets . Multivariate techniques allow for the determination of the pure components within large evolving datasets and as such provide a unique tool for operando spectroscopy.…”

Section: Resultsmentioning

confidence: 99%

“…Owing to the development of time‐resolved operando methods such as X‐ray absorption spectroscopy (XAS), the study of catalysts under the dynamic conditions at which they operate is now possible . The selective catalytic reduction (SCR) of NO x using small pore size and low metal‐loaded Cu−SSZ‐13 is such a reaction that takes place under dynamic conditions and has gained significant attention recently due to the high low‐temperature conversion rate of nitrogen oxides in the presence of NH 3 . The SCR reaction proceeds according to Equation .

true 4 normalN normalO + 4 normalN H_{3} + O_{2} \to 4 N_{2} + 6 H_{2} normalO

…”

Section: Introductionmentioning

confidence: 99%

“…[1][2][3][4][5] The selective catalytic reduction (SCR) of NO x using small pore size and low metal-loaded CuÀ SSZ-13 is such a reaction that takes place under dynamic conditions and has gained significant attention recently due to the high low-temperature conversion rate of nitrogen oxides in the presence of NH 3 . [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21] The SCR reaction proceeds according to Equation (1).…”

Section: Introductionmentioning

confidence: 99%

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Selective Catalytic Reduction of NO with NH₃ on Cu−SSZ‐13: Deciphering the Low and High‐temperature Rate‐limiting Steps by Transient XAS Experiments

et al. 2020

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Cu‐exchanged small‐pore SSZ‐13 catalysts have found wide use for the selective catalytic reduction (SCR) of nitrogen oxides from automotive exhaust gases. The transient working environment of the Cu−SSZ‐13 catalyst during NH3‐SCR requires studying the rate limiting steps under the different operation conditions this catalyst is exposed to. By exploiting time‐resolved operando X‐ray absorption spectroscopy in combination with multivariate analysis we followed the transient speciation of Cu during unsteady state conditions. The results reveal that depending on operating temperature two different rate limiting behaviours inhibit the reduction of NO. At temperatures below 283 °C, ammonia hinders reoxidation of solvated CuI species thereby inhibiting reduction of NO. Whilst at temperatures of 283 °C and above, the reduction of zeolite bound CuII(OH−) is the rate limiting step in the SCR reaction. The results also reveal the presence of two detrimental side reactions occurring, the direct oxidation of zeolite bound CuI at low temperatures and the oxidation of ammonia over Cu at temperatures in excess of 283 °C. Between 250 °C and 350 °C, both side reactions may be present and could explain the dip in the SCR activity typically denoted by the seagull shape.

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Section: Resultssupporting

confidence: 56%

Section: Resultsmentioning

confidence: 98%

Section: Resultsmentioning

confidence: 99%

true 4 normalN normalO + 4 normalN H_{3} + O_{2} \to 4 N_{2} + 6 H_{2} normalO

…”

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Selective Catalytic Reduction of NO with NH₃ on Cu−SSZ‐13: Deciphering the Low and High‐temperature Rate‐limiting Steps by Transient XAS Experiments

et al. 2020

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C−C Bond Formation in Syngas Conversion over Zinc Sites Grafted on ZSM‐5 Zeolite

et al. 2020

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Despite significant progress achieved in Fischer–Tropsch synthesis (FTS) technology, control of product selectivity remains a challenge in syngas conversion. Herein, we demonstrate that Zn2+‐ion exchanged ZSM‐5 zeolite steers syngas conversion selectively to ethane with its selectivity reaching as high as 86 % among hydrocarbons (excluding CO2) at 20 % CO conversion. NMR spectroscopy, X‐ray absorption spectroscopy, and X‐ray fluorescence indicate that this is likely attributed to the highly dispersed Zn sites grafted on ZSM‐5. Quasi‐in‐situ solid‐state NMR, obtained by quenching the reaction in liquid N2, detects C2 species such as acetyl (‐COCH3) bonding with an oxygen, ethyl (‐CH2CH3) bonding with a Zn site, and epoxyethane molecules adsorbing on a Zn site and a Brønsted acid site of the catalyst, respectively. These species could provide insight into C−C bond formation during ethane formation. Interestingly, this selective reaction pathway toward ethane appears to be general because a series of other Zn2+‐ion exchanged aluminosilicate zeolites with different topologies (for example, SSZ‐13, MCM‐22, and ZSM‐12) all give ethane predominantly. By contrast, a physical mixture of ZnO‐ZSM‐5 favors formation of hydrocarbons beyond C3+. These results provide an important guide for tuning the product selectivity in syngas conversion.

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Hydrothermal Stability of Active Sites in Cu‐Exchanged Small‐Pore Zeolites for the Selective Catalytic Reduction of NO_x

Wenig,

Khare,

Jentys

et al. 2024

Angewandte Chemie

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Combining operando X‐ray absorption spectroscopy (XAS) and computational modelling shows unequivocally the distribution of active species in fresh and hydrothermally aged Cu‐CHA and Cu‐AEI zeolites during NH3‐assisted selective catalytic reduction of NOx. Four principal species co‐exist: (i) CuI cations coordinated to NH3, (ii) CuI cations coordinated to the zeolite framework, (iii) solvated CuII cations, and (iv) framework‐coordinated CuII species (CuIIst) formed upon hydrothermal ageing of the zeolite sample. The CuIIst species were only observed in the hydrothermally aged zeolite samples and are formed upon the interaction of hydrated CuII cations with extra‐framework Al generated during the hydrothermal treatment. These sites are inactive for NOx reduction, leading to a decrease in the catalytic performance of the hydrothermally aged zeolites. CuIIst formation was higher in Cu‐CHA (~46%) than in Cu‐AEI (~28%). The better hydrothermal stability of Cu in the AEI framework is attributed to the tortuous channel structure of AEI that hinders the migration of hydrated CuII cations during hydrothermal ageing.

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The dynamic nature of Cu sites in Cu-SSZ-13 and the origin of the seagull NO_x conversion profile during NH₃-SCR

Abstract: Systematic catalytic tests and in situ/operando spectroscopy uncovered structure–performance relationships determining the seagull profile of the NOx conversion for Cu-SSZ-13 catalysts.

Cited by 83 publications

References 73 publications

Selective Catalytic Reduction of NO with NH₃ on Cu−SSZ‐13: Deciphering the Low and High‐temperature Rate‐limiting Steps by Transient XAS Experiments

Selective Catalytic Reduction of NO with NH₃ on Cu−SSZ‐13: Deciphering the Low and High‐temperature Rate‐limiting Steps by Transient XAS Experiments

C−C Bond Formation in Syngas Conversion over Zinc Sites Grafted on ZSM‐5 Zeolite

Hydrothermal Stability of Active Sites in Cu‐Exchanged Small‐Pore Zeolites for the Selective Catalytic Reduction of NO_x

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The dynamic nature of Cu sites in Cu-SSZ-13 and the origin of the seagull NOx conversion profile during NH3-SCR

Abstract: Systematic catalytic tests and in situ/operando spectroscopy uncovered structure–performance relationships determining the seagull profile of the NOx conversion for Cu-SSZ-13 catalysts.

Cited by 83 publications

References 73 publications

Selective Catalytic Reduction of NO with NH3 on Cu−SSZ‐13: Deciphering the Low and High‐temperature Rate‐limiting Steps by Transient XAS Experiments

Selective Catalytic Reduction of NO with NH3 on Cu−SSZ‐13: Deciphering the Low and High‐temperature Rate‐limiting Steps by Transient XAS Experiments

C−C Bond Formation in Syngas Conversion over Zinc Sites Grafted on ZSM‐5 Zeolite

Hydrothermal Stability of Active Sites in Cu‐Exchanged Small‐Pore Zeolites for the Selective Catalytic Reduction of NOx

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The dynamic nature of Cu sites in Cu-SSZ-13 and the origin of the seagull NO_x conversion profile during NH₃-SCR

Selective Catalytic Reduction of NO with NH₃ on Cu−SSZ‐13: Deciphering the Low and High‐temperature Rate‐limiting Steps by Transient XAS Experiments

Selective Catalytic Reduction of NO with NH₃ on Cu−SSZ‐13: Deciphering the Low and High‐temperature Rate‐limiting Steps by Transient XAS Experiments

Hydrothermal Stability of Active Sites in Cu‐Exchanged Small‐Pore Zeolites for the Selective Catalytic Reduction of NO_x