Extraframework Cation Locations in Cu-UZM-35 NH3-SCR Catalyst

Abstract

We have recently demonstrated that divalent copper ions exchanged into the large-pore zeolite UZM-35 with MSE topology (Cu-UZM-35) when hydrothermally aged at 750 degrees C exhibit a considerably wider operating temperature window for NH3-SCR than those into the small-pore zeolite SSZ-13 with CHA topology (Cu-SSZ-13), the current commercial catalyst for this reaction. Here we report the physical states and locations of copper ions in the fresh and 750 degrees C aged forms of Cu-UZM-35 determined using quantitative EPR measurements and synchrotron powder X-ray diffraction and Rietveld analyses. Among the four different cation sites (Cu1-Cu4) identified in fresh Cu-UZM-35, sites Cu3 and Cu4 are easily accessible via 12-ring and 10-ring channels, respectively, allowing their copper ions to serve as the main active sites for NH3-SCR. It was also found that while the Cu2+ ions at site Cu3 remain unchanged even after hydrothermal aging at 750 degrees C, the [Cu(OH)](+) ions at site Cu4 are transformed into CuOx and/or CuAl2O4 species. This led us to conclude that the Cu2+ ions at the former site are mainly responsible for the wide operating temperature window of Cu-UZM-35.