PNNL

Abstract

The influence of copper ion exchange protocol on the SCR activity is quantified within the SSZ-13 zeolite framework. Using the same parent SSZ-13 zeolite, four different exchange protocols are used to assess the effect of the exchange protocol on metal uptake and SCR activity. Large differences in the SCR activity, nearly 30 percentage points at 160 ºC at constant copper content, are observed for different exchange protocols implying that different exchange protocols lead to different copper species. Hydrogen temperature programmed reduction (H2 TPR) on selected samples and infrared spectroscopy of CO binding corroborates this conclusion as the reactivity at 160 ºC is shown to clearly correlate with the intensity of the IR band at 2162 cm-1. DFT-based calculations show that such an IR assignment is consistent with having CO adsorbed on a Cu(I) cation within an eight-membered ring. This work shows that SCR activity can be influenced by the ion exchange process, and that an ion-exchange process that leads to copper trimers as reported in the literature results in the most active catalyst. This points to an as yet not recognized means to tailor catalyst activity.