Electron Paramagnetic Resonance: A Powerful Tool for Monitoring Working Catalysts

EPR spectroscopy is a versatile tool for online monitoring of catalytic reactions that include paramagnetic species either within catalysts (e.g., transition metal ions, defects) or among reaction intermediates (radicals). This review provides a summary of experimental conditions and apparatus used to characterize working solid catalysts by EPR spectroscopy. Opportunities for applying this technique during synthesis and equilibration of solid catalysts as well as during their operation in gas- and liquid-phase reactions are illustrated by examples, including, for example, vanadia-containing oxides and FeMFI zeolites. The use of spin probes for the following synthesis procedures and spin traps for detecting hydrocarbon radicals in photocatalysis is illustrated. Benefits that arise from simultaneous coupling of EPR spectroscopy with UV-vis and Raman spectroscopies are also presented. Opportunities and limitations of the technique for applications in catalysis are evaluated and ideas for future improvements are suggested.