As the state-of-the-art catalyst for the selective catalytic reduction (SCR) of NOx, Cu-CHA has been extensively investigated in both its practical and fundamental aspects. Among the latter, how Z2Cu2+, an active site for SCR, participates in low-temperature (LT) SCR reactions remains debated. Here, we propose a scheme involving the hydrolysis of Z2Cu2+ to ZCu2+(OH)-, a thermodynamically and kinetically favorable process under LT-SCR conditions, based on multiple pieces of evidence from a probe reaction (transient CO oxidation), transient Cu2+ reduction kinetic runs, in situ FTIR spectroscopy, and first-principles calculations. Such an integrated investigation reveals unambiguously that the hydrolysis of Z2Cu2+ to ZCu2+(OH)- occurs facilely in the presence of NH3, which may thus reconcile the identical quadratic kinetics of Z2Cu2+/ZCu2+(OH)- reduction with the inactivity of Z2Cu2+ in the formation of Cu2+ pairs. Accordingly, we highlight that NH3-assisted hydrolysis plays a critical role in LT-SCR and should be taken into account especially when discussing SCR reaction details over Z2Cu2+.

Unraveling the Hydrolysis of Z2Cu2+to ZCu2+(OH)-and Its Consequences for the Low-Temperature Selective Catalytic Reduction of NO on Cu-CHA Catalysts

Hu W.;Iacobone U.;Gramigni F.;Liu S.;Nova I.;Tronconi E.
2021-01-01

Abstract

As the state-of-the-art catalyst for the selective catalytic reduction (SCR) of NOx, Cu-CHA has been extensively investigated in both its practical and fundamental aspects. Among the latter, how Z2Cu2+, an active site for SCR, participates in low-temperature (LT) SCR reactions remains debated. Here, we propose a scheme involving the hydrolysis of Z2Cu2+ to ZCu2+(OH)-, a thermodynamically and kinetically favorable process under LT-SCR conditions, based on multiple pieces of evidence from a probe reaction (transient CO oxidation), transient Cu2+ reduction kinetic runs, in situ FTIR spectroscopy, and first-principles calculations. Such an integrated investigation reveals unambiguously that the hydrolysis of Z2Cu2+ to ZCu2+(OH)- occurs facilely in the presence of NH3, which may thus reconcile the identical quadratic kinetics of Z2Cu2+/ZCu2+(OH)- reduction with the inactivity of Z2Cu2+ in the formation of Cu2+ pairs. Accordingly, we highlight that NH3-assisted hydrolysis plays a critical role in LT-SCR and should be taken into account especially when discussing SCR reaction details over Z2Cu2+.
2021
Cu speciation
Cu-CHA
hydrolysis
low-temperature SCR
Z
2
Cu
2+
ZCu
2+
(OH)
-
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11311/1208077
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