(349ag) A Kinetic Modelling Strategy for Interrogating NOx Selective Catalytic Reduction on Cu-Exchanged Zeolites

The selective catalytic reduction (SCR) of NOx with NH3 using Cu-Chabazite (CHA) zeolites is a commercial technology for controlling diesel emissions. SCR proceeds through a redox mechanism in which NO and NH3 reduce Cu(II) and O2 oxidizes Cu(I). Steady-state kinetic rate observations, transient oxidation experiments, and metadynamics simulations are all consistent with an oxidation step that involves pairing of Cu(I) cations whose mobility is regulated by electrostatic tethering to anionic framework Al sites. This tethering introduces a kinetic dependence on effective diffusion volume, the behavior of which cannot be captured through conventional mean-field kinetic models. Here we introduce a coarse-grained kinetic Monte Carlo (kMC) strategy to describe steady-state and transient SCR kinetics on Cu-CHA. The model incorporates a non-mean-field contribution from the mobility and distance-wise dependent pairability on the Cu(I) oxidation kinetics. We show that this model can recover apparent Cu rate orders and residual Cu(I) densities qualitatively consistent with observation. We use a Bayesian optimization scheme to extract model parameters from experimentally observed SCR rates across a range of materials of varying composition. An analysis of their dependence on framework Al anion and extra-framework Cu cation densities allows us to extract insights into the microscopic processes that control observed rates, pointing the way towards more effective materials design.