Copper Coordination to Water and Ammonia in Cu<sup>II</sup>-Exchanged SSZ-13: Atomistic Insights from DFT Calculations and in Situ XAS Experiments

Kerkeni, Boutheı̈na; Berthout, David; Berthomieu, Dorothée; Doronkin, Dmitry E.; Casapu, Maria; Grunwaldt, Jan‐Dierk; Chizallet, Céline

doi:10.1021/acs.jpcc.8b03572

Cited by 32 publications

(55 citation statements)

References 77 publications

(237 reference statements)

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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%

“…At low temperature (190 and 225 °C, Figure a,b), the introduction of NO leads to an increase in concentration of solvated Cu I species. It has also been noted elsewhere that the strength of reduction is increased in a gas mixture containing both NO and NH 3 . Furthermore the stability, and as such lifetime, of the solvated Cu I species is increased by the presence of NO in the gas feed.…”

Section: Resultsmentioning

confidence: 61%

“…The loss of coordinating ligands upon heating has also previously been observed elsewhere. [9,10,48] Transient speciation changes are observed when the steady-state SCR conditions are perturbed through removal of NH 3 from the gas feed. A transient increase in solvated square planar Cu II species (red) is observed directly subsequent to NH 3 cut-off at 190 and 225°C.…”

Section: Resultsmentioning

confidence: 99%

“…It has also been noted elsewhere that the strength of reduction is increased in a gas mixture containing both NO and NH 3 . [15,48,50] Furthermore the stability, and as such lifetime, of the solvated Cu I species is increased by the presence of NO in the gas feed. This may be due to solvated Cu I species containing both coordinating NH 3 and NO ligands at low temperature, as proposed by the Janssens mechanism (Figure 1).…”

Section: Resultsmentioning

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: 61%

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

See 2 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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“…The Gibbs free energies were calculated according to the approach detailed in ref. 32 by considering the rotational, translational, and vibrational degrees of freedom for gas-phase water and ammonia, and the vibrational degrees of freedom only for the zeolite models. The Gibbs free energy values were calculated at a temperature domain between 398 and 698 K and a pressure of 1 Atm.…”

Section: Methodsmentioning

confidence: 99%

Modeling Ammonia and Water Co-Adsorption in Cu^I-SSZ-13 Zeolite Using DFT Calculations

Petitjean

Chizallet

Berthomieu

2018

Ind. Eng. Chem. Res.

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Cu-SSZ-13 efficiently catalyzes the selective catalytic reduction (SCR) of NO by NH 3 but the structure of the active site and, particularly, the redox state of the copper (+I or +II) are still debated. This paper focuses on the possible contribution of Cu I species with a theoretical investigation of adsorption and co-adsorption of NH 3 and H 2 O on Cu I species using quantum chemistry and including dispersion forces. The calculations show that Cu I clearly migrates upon adsorption of NH 3. While Cu I is initially in close interaction with the zeolite framework, it preferentially forms coordination bonds with NH 3 and interacts with the zeolite in its second coordination sphere. The same tendency is calculated with H 2 O, even if the binding energy of H 2 O with Cu I is lower than with NH 3. All the Cu I complexes sit in the cage containing the 8 MR. The confined Cu I complexes interact with the zeolite framework through several H-bonds donated by the NH or OH bonds of the ligands. In the experimental temperature and pressure domain of SCR conditions, calculated phase diagrams show that coordination number of two is predicted for the co-adsorption of NH 3 and H 2 O on Cu I. For pure H 2 O, few stable domains for hydrated species containing Cu I are calculated in contrast with pure NH 3. Finally, the calculated phase diagrams on Cu I-SSZ-13 are discussed together with the more documented diagrams of Cu II-SSZ-13 and recent experimental characterizations, providing a wider picture of the real catalyst in SCR conditions. ORCID D.

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In Situ Spectroscopic Studies on the Redox Cycle of NH₃−SCR over Cu−CHA Zeolites

et al. 2020

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The selective catalytic reduction of NO with ammonia (NH3−SCR) catalyzed by Cu−CHA zeolites is thoroughly investigated using in situ spectroscopic experiments combined with on‐line mass spectroscopy (MS) under steady‐state NH3−SCR conditions and transient conditions for Cu(II)/Cu(I) redox cycles. Quantitative analysis of the in situ XANES spectra of Cu−CHA under steady‐state conditions of NH3−SCR show that NH3‐coordinated Cu(II) species is the dominant Cu species at low temperatures (100–150 °C). At higher temperatures, Cu(II) species and [Cu(NH3)2]+ complex coexist, possibly because the rate of the Cu(II)→Cu(I) reduction step is comparable to that of the Cu(I)→Cu(II) oxidation step. In situ XANES, IR/MS, and UV‐vis/MS experiments on the reduction half cycle demonstrate that the reduction of Cu(II) species occurs via the reaction of NH3‐liganded Cu(II) with NO to yield N2 and H2O. For the oxidation half cycle, in situ XANES experiments of Cu(I) oxidation in 10 % O2 at 200 °C indicate that an increased density in CHA zeolite exhibits a higher oxidation rate. In situ UV‐vis experiments of Cu(I) reoxidation using different mixtures of oxidant feed gas demonstrate the key role of O2 in the oxidation cycle. It is suggested that the reoxidation of Cu(I) to Cu(II) species occurs with only O2 as the oxidant, and a high Cu density in CHA zeolite promotes SCR activity by enhancing the oxidative activation of Cu(I) to Cu(II) during the catalytic cycle.

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Copper Coordination to Water and Ammonia in Cu^II-Exchanged SSZ-13: Atomistic Insights from DFT Calculations and in Situ XAS Experiments

Cited by 32 publications

References 77 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

Modeling Ammonia and Water Co-Adsorption in Cu^I-SSZ-13 Zeolite Using DFT Calculations

In Situ Spectroscopic Studies on the Redox Cycle of NH₃−SCR over Cu−CHA Zeolites

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Copper Coordination to Water and Ammonia in CuII-Exchanged SSZ-13: Atomistic Insights from DFT Calculations and in Situ XAS Experiments

Cited by 32 publications

References 77 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

Modeling Ammonia and Water Co-Adsorption in CuI-SSZ-13 Zeolite Using DFT Calculations

In Situ Spectroscopic Studies on the Redox Cycle of NH3−SCR over Cu−CHA Zeolites

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Resources

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Copper Coordination to Water and Ammonia in Cu^II-Exchanged SSZ-13: Atomistic Insights from DFT Calculations and in Situ 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

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

Modeling Ammonia and Water Co-Adsorption in Cu^I-SSZ-13 Zeolite Using DFT Calculations

In Situ Spectroscopic Studies on the Redox Cycle of NH₃−SCR over Cu−CHA Zeolites