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

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 Z(2)Cu(2+), an active site for SCR, participates in low-temperature (LT) SCR reactions remains debated. Here, we propose a scheme involving the hydrolysis of Z(2)Cu(2+) to ZCu(2+)(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 Z(2)Cu(2+) to ZCu(2+)(OH)(-) occurs facilely in the presence of NH3, which may thus reconcile the identical quadratic kinetics of Z(2)Cu(2+)/ZCu(2+)(OH)(-) reduction with the inactivity of Z(2)Cu(2+) 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 Z(2)Cu(2+).