Mechanism-based kinetic modeling of Cu-SSZ-13 sulfation and desulfation for NH3-SCR applications

A multi-site kinetic model was developed to predict the effect of sulfur dioxide on Cu-SSZ-13 for the NH3 selective catalytic reduction (NH3-SCR) of NOx. To develop a mechanism-based kinetic model, two different Cu sites were assumed describing the formation–decomposition of S intermediates i.e. copper bisulfite on ZCuOH (site 1, S1) and ammonium sulfate on Z2Cu (site 2, S2). Transient kinetics of SO2 interactions with Cu-SSZ-13 were simulated, exploiting SO2 and SO2 + NH3 temperature programmed desorption (TPD) experiments. Besides S1 and S2, a 3rd site was assumed to account for the Bronsted acid site and NH3 adsorption on that site. The model also accounts for NH3-SCR activity over fresh, sulfated and regenerated (at 550 °C) Cu-SSZ-13 samples with different Si : Al and Cu : Al ratios. Finally, the model was capable of describing fresh SCR for commercial and prepared samples without tuning any kinetic parameters, but by only varying ZCuOH and ZCu site densities obtained utilizing H2 temperature programmed reduction (H2-TPR) and inductively coupled plasma optical emission spectroscopy (ICP-OES).