A review on the characterization of metal active sites over Cu-based and Fe-based zeolites for NH-SCR.

Cu-based and Fe-based zeolites are promising catalysts for NH-SCR due to their high catalytic activity, wide temperature window and good hydrothermal stability, while the detailed investigation of NH-SCR mechanism should be based on the accurate determination of active metal sites. This review systematically summarizes the qualitative and quantitative determination of metal active sites in Cu-based or Fe-based zeolites for NH-SCR reactions based on advanced characterization methods such as UV-vis absorption (UV-vis), temperature-programmed reduction with H (H-TPR), X-ray photoelectron spectroscopy (XPS), X-ray absorption fine structure spectroscopy (XAFS), Infrared spectroscopy (IR), Electron paramagnetic resonance (EPR), Mössbauer spectroscopy and DFT calculations. The application and limitations of different characterization methods are also discussed to provide insights for further study of the NH-SCR reaction mechanism over metal-based zeolites.