Effects of zeolite framework topology on Cu(I) oxidation and Cu(II) reduction kinetics of NOx selective catalytic reduction with NH3

The low-temperature (<523 K) selective catalytic reduction (SCR) of nitrogen oxides proceeds on Cu-zeolites. Cu cations are NH3 solvated, ionically tethered to framework Al centers, and partially mobile within microporous voids, influencing the ability of Cu ions to pair within voids to close the SCR oxidation half-cycle. The influence of zeolite framework topological features on pairability and Cu-normalized SCR reactivity is not well understood. We combine steady-state kinetics and operando and transient X-ray absorption (XAS) measurements on Cu-zeolites chosen to probe the influence of pore structure and dimensionality on SCR rate constants and fractions of SCR-active Cu sites, together with statistical simulations and ab initio dynamics simulations, to show that changes in pore size and shape among 3D cage-window zeolites have subtle effects on Cu ion pairability and SCR reactivity but that decreasing pore dimensionality to 2D or 1D networks imposes more severe restrictions on Cu ion pairability and SCR reactivity.