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

Abstract

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 NO_x. 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 Brønsted 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).