On the various Cu-redox pathways and O2-mediated Bronsted-to-Lewis adsorbed-NH3 redistribution under SCR half-cycle conditions

Deka, Dhruba J.; Daya, Rohil; Joshi, Saurabh Y.; Partridge, William P.

doi:10.1016/j.apcata.2022.118656

Cited by 11 publications

(17 citation statements)

References 32 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The oxidation process shows faster dynamics at higher temperatures, as reflected by the more rapid approach to the plateau at 200 °C. Furthermore, complete reoxidation was reached in all cases after exposing the reduced Cu-CHA25 catalyst to oxygen for 1 h, suggesting that O 2 (+H 2 O) alone has the potential to mediate OHC, in agreement with the literature. ,,− …”

Section: Resultssupporting

confidence: 89%

“…Notably, no dependence on the NO concentration was considered in the OHC rate model (NO silent oxidation mechanism): this implies that NO consumption (and the mirrorlike N 2 production) during the Standard SCR reaction is only ascribed to the RHC. Moreover, this assumption also suggests that: (i) NO is not relevant for the catalyst reoxidation at low temperature, in agreement with refs and ; (ii) the overall stoichiometry governing the redox cycle of the Cu active sites in Standard SCR involves a 1:1 ratio between Cu cycling and NO consumed in each cycle, at variance with the 1:2 Cu to NO ratio claimed in several publications ,,, but consistent with the mechanistic proposals in ref .…”

Section: Resultssupporting

confidence: 88%

“…Activation energies ( E ACT ) of 25 ± 1.8 kJ/mol and 79 ± 12.5 kJ/mol were computed for the RHC and OHC, respectively; the lower E ACT for RHC is consistent with the temperature effect on Cu II –Cu I partitioning at steady-state Standard SCR, as discussed above. Significantly different activation energy estimates were reported in several publications, ,− ,,, which however assumed different RHC and OHC mechanisms involving a Cu:NO = 1:2 overall stoichiometry for the Standard SCR Cu-redox cycle, in contrast with the experimental results herein reported, and in some cases accounted also for the ammonia coverage dependence, while we assumed the RHC and OHC rates to be zeroth-order in ammonia, as described in Section . Therefore, a clean comparison of the activation energy estimates is problematic.…”

Section: Resultsmentioning

confidence: 84%

“…where k RHC and k OHC are the apparent reduction and oxidation rate constants and y NO and P normalO 2 are the NO molar fraction and oxygen partial pressure, respectively, which are normalized by the reference feed concentrations (i.e., NO = 500 ppm and O 2 = 8% v/v). Concerning the reduction reaction, we assumed a zeroth reaction order in NH 3 , consistent with the work of Partridge et al In addition, a first-order dependence on NO and a second-order dependence on the fraction of oxidized Cu sites were adopted in accordance with our previous work , and other recent literature. , Moreover, regarding the oxidation rate, a second-order dependence on the fraction of the reduced Cu sites was assumed, as also proposed by several research groups. , …”

Section: Materials and Methodsmentioning

confidence: 75%

“…The latter activates an O 2 molecule, leading to the formation of an oxidized and mobile μ-peroxo diamino Cu II -dimer species (i.e., Z 2 Cu II 2 (NH 3 ) 4 O 2 ). , According to the literature, such an intermediate would further react with gaseous NO and adsorbed ammonia in the RHC to produce nitrogen and water . Recent works by Tronconi, Gao, and co-workers − (through dedicated transient tests, kinetic modeling analysis, and DFT calculations) and Partridge, Daya, and co-workers − (through dedicated transient experiments and kinetic modeling analysis) demonstrated the low-temperature reduction mechanism to involve pairs of ZCu II OH(NH 3 ) 3 placed in the same zeolite cage, of which the reaction with NO and NH 3 leads to the reduction of the Cu sites. These findings emphasize the inadequacy of the single-site mechanisms proposed in the literature for the Cu II reduction under low-temperature NH 3 -SCR conditions. ,, …”

Section: Introductionmentioning

confidence: 99%

See 4 more Smart Citations

Dual-Site RHC and OHC Transient Kinetics Predict Low-T Standard SCR Steady-State Rates over a Cu-CHA Catalyst

et al. 2023

View full text Add to dashboard Cite

The reduction (RHC: Cu II → Cu I ) and oxidation (OHC: Cu I → Cu II ) half-cycles of low-temperature (150−200 °C) NH 3 -selective catalytic reduction (SCR) were investigated by transient response methods over a model Cu-CHA catalyst (Cu loading = 1.8% w/w; silica to alumina ratio = 25). In line with previous findings: i) RHC proceeded via second-order kinetics in Cu II and with an equimolar stoichiometry between Cu II reduced and NO consumed; ii) complete reoxidation of reduced NH 3solvated Cu sites was achieved by exposing the catalyst to O 2 + H 2 O only, no other species (e.g., NO) were found to be relevant to the OHC pathway. Dedicated kinetic tests highlighted a secondorder dependence of the OHC rate on Cu I and a first-order dependence on O 2 . Coupling the RHC and OHC kinetic models, independently developed from transient tests, resulted in an accurate description of Standard SCR turnovers, predicting steady-state NO conversion, N 2 formation, and bed-average Cu-oxidation states, as well as light-off and extinction transients closely consistent with experimental measurements. These results demonstrate the rational dissection of the complex steady-state SCR reaction network into two redox half-cycles and provide a stoichiometrically and kinetically consistent closure of the Standard SCR redox cycle over Cu-CHA catalysts.

show abstract

Section: Resultssupporting

confidence: 89%

Section: Resultssupporting

confidence: 88%

Section: Resultsmentioning

confidence: 84%

Section: Materials and Methodsmentioning

confidence: 75%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Dual-Site RHC and OHC Transient Kinetics Predict Low-T Standard SCR Steady-State Rates over a Cu-CHA Catalyst

et al. 2023

View full text Add to dashboard Cite

show abstract

The [(NH₃)₄Cu₂O₂]²⁺‐Peroxo Complex as the Key Intermediate for NH₃‐SCR Activity and Deactivation of Cu‐CHA Catalysts.

Janssens,

Borfecchia,

Lomachenko

et al. 2024

ChemCatChem

View full text Add to dashboard Cite

In NH3‐SCR over Cu‐CHA catalysts in the low‐temperature range 150‐300 °C, the activation of oxygen occurs via oxidation of a pair of mobile (NH3)2CuI‐complexes located in the cages of the zeolite. In this step, a reactive [(NH3)4Cu2O2]2+‐peroxo complex (μ‐η2,η2‐peroxo diamino dicopper(II)‐complex) is formed. The chemistry of this complex determines several catalytic properties of the Cu‐CHA catalyst. The reaction of NO with the [(NH3)4Cu2O2]2+‐peroxo complex governs the NH3‐SCR activity. A reaction of the [(NH3)4Cu2O2]2+‐peroxo complex with ammonia hinders the reaction of NO with the complex, thus leading to an inhibition of the NH3‐SCR reaction. Finally, the deactivation in presence of SO2 is due to a reaction of SO2 with the [(NH3)4Cu2O2]2+‐peroxo complex, leading to the formation of Cu‐S compounds in the catalyst. In this review, the characterization and the reactions of the [(NH3)4Cu2O2]2+‐peroxo complex with NO, NH3, and SO2, and mean‐field kinetic models based on first principles calculations for NH3‐SCR activity and SO2 poisoning are discussed.

show abstract

A Strategic NH3-Dosing Approach for the Minimization of N2O Production During NH3-SCR Reactions over Cu-SSZ-13 Catalysts

Nasello,

Usberti,

Nova

et al. 2024

Emiss. Control Sci. Technol.

View full text Add to dashboard Cite

The undesired production of N2O during NH3-SCR reactions is investigated over a reference commercial Cu-CHA catalyst. Steady-state experiments performed in the 150–500 °C temperature range exhibit a bimodal trend in the N2O formation profile, confirming the existence of two different reaction mechanisms occurring at low and high temperatures. Focusing on a low-to-medium T-range, N2O production, usually ascribed to NH4NO3 formation and decomposition, increases with the NO2/NOx ratio. However, an excess of NO2 leads to a decrease in the N2O release due to ammonium nitrate deposition and catalyst clogging phenomena. Steady-state and dynamics experiments show the promoting effect of both NH3 feed concentration and NH3 storage on N2O production at T > 200 °C. Surprisingly, N2O decreases with increasing NH3/NOx ratio at lower temperature. A novel approach based on the strategic injection of NH3 is also applied to mitigate the N2O formation while maintaining high deNOx activity. Remarkably, complete NOx conversion and ~ 11% N2O saving are achieved (with inlet NO2/NOx = 0–0.5) at temperatures exceeding 200 °C; in addition, a peculiar behavior is observed in the N2O profile, which increases and decreases when adding and removing NH3 from the feed, respectively. Notably, the opposite trend is observed in the N2O profile at 200 °C. When under Standard SCR conditions, this so far unreported observation challenges the NH4NO3 formation route for N2O and suggests the existence of different controlling phenomena at different temperature regimes: i) the Cu/redox chemistry at T ≤ 200 °C and ii) the NH3 storage at higher temperature, ideally up to 300 °C.

show abstract

On the various Cu-redox pathways and O2-mediated Bronsted-to-Lewis adsorbed-NH3 redistribution under SCR half-cycle conditions

Cited by 11 publications

References 32 publications

Dual-Site RHC and OHC Transient Kinetics Predict Low-T Standard SCR Steady-State Rates over a Cu-CHA Catalyst

Dual-Site RHC and OHC Transient Kinetics Predict Low-T Standard SCR Steady-State Rates over a Cu-CHA Catalyst

The [(NH₃)₄Cu₂O₂]²⁺‐Peroxo Complex as the Key Intermediate for NH₃‐SCR Activity and Deactivation of Cu‐CHA Catalysts.

A Strategic NH3-Dosing Approach for the Minimization of N2O Production During NH3-SCR Reactions over Cu-SSZ-13 Catalysts

Contact Info

Product

Resources

About

On the various Cu-redox pathways and O2-mediated Bronsted-to-Lewis adsorbed-NH3 redistribution under SCR half-cycle conditions

Cited by 11 publications

References 32 publications

Dual-Site RHC and OHC Transient Kinetics Predict Low-T Standard SCR Steady-State Rates over a Cu-CHA Catalyst

Dual-Site RHC and OHC Transient Kinetics Predict Low-T Standard SCR Steady-State Rates over a Cu-CHA Catalyst

The [(NH3)4Cu2O2]2+‐Peroxo Complex as the Key Intermediate for NH3‐SCR Activity and Deactivation of Cu‐CHA Catalysts.

A Strategic NH3-Dosing Approach for the Minimization of N2O Production During NH3-SCR Reactions over Cu-SSZ-13 Catalysts

Contact Info

Product

Resources

About

The [(NH₃)₄Cu₂O₂]²⁺‐Peroxo Complex as the Key Intermediate for NH₃‐SCR Activity and Deactivation of Cu‐CHA Catalysts.