Soft X-ray absorption spectroscopy in heterogeneous catalysis Review Article

Soft X-ray absorption spectroscopy proved to be a very powerful tool in different disciples and particularly in heterogeneous catalysis. The fine structure of the transition metals, which constitutes the metallic part of catalysts, is present at the L- and M-edges, while a shoulder is generally measured at the K-edge (3d and 4d transition metals). The observation of such fine details associated with the emergence of a significant theoretical formalism, allows a more precise description of the structural and electronic characteristics of this family of materials as compared to the one obtained through more classical Exafs based on hard X-ray photons. Moreover, X-ray absorption spectra can be collected at the K-edge of light elements such as carbon, nitrogen or oxygen. Thus, adsorption process of molecules of major interest in heterogeneous catalysis can be studied completely from the two actors of the chemical bond leading to a precise knowledge of intermediate species. At first, a brief presentation of the theoretical formalism as well as a description of several experimental devices implemented at LURE and dedicated to soft X-ray absorption are done. Then, different publications based on the analysis of soft X-ray spectra collected either at the K-edge of light elements or at the L- and M-edges of transition metals are presented. Finally, we will take some selected examples to demonstrate the nature of information obtained through this technique and discuss the advantages and the limits of such approach.