43. Case Study 1: Modulation Excitation Spectroscopy (MES)

Selective catalytic reduction (SCR) is an emission control technology that has continuously remained at the forefront of research using spectroscopy. While steady-state studies significantly advanced our mechanistic knowledge of SCR in the past, they proved to be not the best-suited approach to elucidate the reaction cycle conclusively. Nowadays, transient-response experimentation – especially modulated excitation spectroscopy (MES) – is rapidly emerging as an alternative due to its improved sensitivity and analytical capabilities. Here we present a selection of recent SCR-related studies that clearly illustrates the advantages of MES. Coupled to vibrational methods such as infrared or Raman spectroscopy, MES can amplify weak but dynamic signals, resolve overlapping peaks, discriminate between active and merely responsive sites, and enable the detection of intermediate species. Thanks to these improved features, MES can extend our molecular view of SCR to unprecedented levels that are not attainable using steady-state measurements.