Cu Siting in Zeolite SCR Catalysts: An EPR Study

Cu-zeolite materials are an important class of catalysts for the selective catalytic reduction (SCR) of NOx present in lean burn engines. They are used in urea-based technologies for Diesel engines, and there is increased interest in chabazite-like structures for NH3-based SCR for both Diesel and gasoline-based engines. Improvements in existing technologies and development of new zeolite catalysts require further understanding of the Cu-species present as well as of their catalytic role.

We present a detailed Electron Paramagnetic Resonance (EPR) spectroscopy study of fresh and deactivated Cu-zeolite catalysts (operated at high space velocities during NOx SCR under wet conditions (1)). Analysis of the spectra allows us to determine the Cu siting and relative occupancy of zeolite exchange sites as a Cu-ZSM5 ages. UV-Vis spectroscopy is also used to study Cu-siting. Extension to other zeolites will be included as well as a discussion of their relative stability under wet SCR operation.

1- S.A. Gómez, A. Campero, A. Martínez-Hernández and G.A. Fuentes, Appl.Catal. A: General, 197 (2000) 157-164.