Recent Advances in the Application of Mößbauer Spectroscopy in Heterogeneous Catalysis

Mößbauer spectroscopy is a high-resolution spectroscopic technique suitable for investigating solid catalysts that contain nuclei which exhibit the Mößbauer effect. As integral part of a solid, the Mößbauer nucleus plays the role of a probe that interacts, by virtue of its magnetic and electric moments, with the surrounding fields created by unpaired electrons and ionic charges. The Mößbauer effect can be used to quantitatively measure these hyperfine interactions with unprecedented energy resolution, and a series of gamma-resonance techniques are based on this effect. These techniques allow the determination of the catalyst phase, the particle size, the structure, and the oxidation state in the bulk and at the surface of the catalyst, and they provide additional information that is difficult to acquire with other techniques. In this review, the principles of Mößbauer spectroscopy, the observed effects and hyperfine interactions, and in situ techniques are presented in compact form. The search for correlations between catalytic behavior and the structure and composition of catalysts motivate Mößbauer measurements under in situ conditions. The recent advances made by application of Mößbauer spectroscopy in catalysis are summarized in detail, including results from energy catalysis, environmental catalysis, aerospace catalysis, petrochemistry, and photocatalysis. Finally, brief insight into biological catalysis is given by reviewing the latest applications of synchrotron radiation nuclear gamma-resonance elastic and inelastic scattering spectroscopies that have recently been implemented at synchrotron rings of the third generation.