Electron-Paramagnetic-Resonance Spectroscopy of Catalytic Surfaces

A review is presented of the application of electron paramagnetic resonance (EPR) spectroscopy to study surfaces of catalytic interest. Spectra of Mo(V) in supported molybdena catalysts illustrate how EPR can assist in the characterization of such materials. The spectra of an adsorbed stable radical, the superoxide ion, are used to show how surface sites on catalysts can be probed by EPR. Unstable radicals which are conceivable intermediates in catalytic reaction mechanisms can be identified via spin trapping experiments, either chemical or matrix isolation. The mobility of adsorbed radicals on surfaces can be studied by EPR. Finally, recent progress in observing EPR spectra from well-defined single-crystal surfaces is discussed.