Quantification of Exchanged Copper Species in Cu-Chabazite Zeolite using Cryogenic Probe Infrared Spectroscopy

Abstract

The development of a low temperature (−160 °C) NO adsorption technique is disclosed that avoids the chemical conversion of the probe molecule at room temperature. The observed IR peaks for Cu+(NO)2 and Cu2+(NO) species can be used to quantify the amount of exchanged copper species in a broad range of samples, including a wash-coated honeycomb. Calibration curves for Cu+(NO)2 and Cu2+(NO) are determined for copper loadings up to 3.99 wt% with Silica-to-Alumina Ratio (SAR) of 16–22, and quantitative agreement with the complementary hydrogen Temperature Programmed Reduction (H2-TPR) results is established. This methodology allows to identify different Cu species in Cu-CHA, such as Z2Cu(II), Z1Cu(II)OH and Cu dimers, based on their distinct IR signatures. In addition, the perturbed T−O−T framework vibration – characterized at 400 °C – can also be used as a complimentary method to quantify Z2Cu(II) species.